Apparatus and method for analysing the condition of a machine having a rotating part

ABSTRACT

An apparatus for analysing the condition of a machine having a part rotating with a speed of rotation (f ROT ), comprising: a first sensor ( 10 ) adapted to generate an analogue electric measurement signal (S EA ) dependent on mechanical vibrations (V MD ) emanating from rotation of said part; an analogue-to-digital converter ( 40, 44 ) adapted to sample said analogue electric measurement signal (S EA ) at an initial sampling frequency (f S ) so as to generate a digital measurement data signal (SMD,  SENV ) in response to said received analogue electric measurement signal (S EA ); a device ( 420 ) for generating a position signal (Ep) having a sequence of position signal values (P (i) ) for indicating momentary rotational positions of said rotating part; and a speed value generator ( 601 ) being adapted for recording a time sequence of said position signal values (P (i) ) such that there are angular distances (delta-FI p1-p2 , delta-FI p2-p3 ) and corresponding durations (delta-T p1-p2 ; delta-T p2-p3 ) between at least three consecutive position signals (P 1 , P 2 , P 3 ) wherein the speed value generator ( 601 ) operates to establish at least two momentary speed values (VT 1 ; VT 2 ) based on said angular distances (delta-FI p1-p2 , delta-FI p2-p3 ) and said corresponding durations (delta-T p1-p2 ; delta-T p2-p3 ), and wherein further momentary speed values for the rotational part ( 8 ) are established by interpolation between the at least two momentary speed values (VT 1 , VT 2 ).

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method for analysing the condition ofa machine, and to an apparatus for analysing the condition of a machine.The invention also relates to a system including such an apparatus andto a method of operating such an apparatus. The invention also relatesto a computer program for causing a computer to perform an analysisfunction.

Description of the Related Art

Machines with moving parts are subject to wear with the passage of time,which often causes the condition of the machine to deteriorate. Examplesof such machines with movable parts are motors, pumps, generators,compressors, lathes and CNC-machines. The movable parts may comprise ashaft and bearings.

In order to prevent machine failure, such machines should be subject tomaintenance, depending on the condition of the machine. Therefore theoperating condition of such a machine is preferably evaluated from timeto time.

SUMMARY OF THE INVENTION

An aspect of the invention relates to the problem of enabling preventionof unexpected machine breakdown due to mechanical wear or damage in amachine having a part rotatable with a speed of rotation. In particular,an aspect of the invention relates to the problem of enabling animproved ability to detect mechanical wear or damage in a machine havinga part that rotates with a variable speed of rotation.

This problem is addressed by an apparatus for analysing the condition ofa machine having a part rotating with a speed of rotation (f_(ROT)),comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(s)) so as to generate a digital measurement data signal(S_(MD), S_(ENV), S_(RED1)) in response to said received analogueelectric measurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part; and

a speed value generator (601) being adapted to record

-   -   a time sequence of measurement sample values (Se(i), S_((j))) of        said digital measurement data signal (S_(MD), S_(ENV),        S_(RED1)), and    -   a time sequence of said position signal values (P(i)) such that        there are angular distances (delta-FI_(p1-p2), delta-FI_(p2-p3))        and corresponding durations (delta-T_(p1-p2); delta-T_(p2-p3))        between at least three consecutive position signals (P1, P2,        P3), and    -   time information (i, dt; j) such that an individual measurement        data value (S_((j))) can be associated with data indicative of        time (i, dt; j) and angular position (P(i)); and wherein

the speed value generator (601) operates to establish at least twomomentary speed values (VT1; VT2) based on said angular distances(delta-FI_(p1-p2), delta-FI_(p2-p3)) and said corresponding durations(delta-T_(p1-p2); delta-T_(p2-p3)), and wherein

the speed value generator (601) operates to establish further momentaryspeed values (f_(ROT)(j) for the rotational part (8) by interpolationbetween the at least two momentary speed values (VT1, VT2) such that aninterpolated further momentary speed value (f_(ROT)(j)) is indicative ofthe rotational speed at the moment of detection of at least one of saidrecorded measurement sample values (Se(i), S_((j))); and

a decimator (310, 470, 470B) for generating a second digital signal(S_(RED2), R), having a reduced sampling frequency (f_(SR2)), inresponse to said digital measurement data signal (S_(MD), S_(ENV),S_(RED1)), and

an evaluator (230; 290, 290T; 294, 290, 290F) for performing a conditionanalysis function (F1, F2, Fn) for analysing the condition of themachine dependent on said second digital signal (S_(RED2)); wherein

said decimator (470, 470B) is adapted to perform said decimationdependent on said interpolated further momentary speed value(f_(ROT)(j)), VT1, VT2, f_(ROT)).

This solution advantageously enables the delivery of a time sequence ofmeasurement sample values (Se(i), S_((j))) wherein an individualmeasurement sample value (Se(i), S_((j))) is associated with a speedvalue (f_(ROT)(j)), Vpi) indicative of a speed of rotation of said ofsaid rotational part (8) at the time of detection of the sensor signal(S_(EA)) value corresponding to that data value (Se(i), S_((j))). Theuse of interpolation for generating the speed of rotation values enablesan advantageously small level of inaccuracy even during an accelerationphase.

The provision of a sequence of measurement sample values (Se(i),S_((j))) associated with corresponding speed of rotation values havingsmall levels of inaccuracy enables an improved performance, in terms ofreduced or eliminated smearing of the measurement sample values, by thesubsequent decimation process during acceleration phases. The reduction,or elimination, of smearing of the measurement sample values resultingfrom the decimation process enables an improved performance of thecondition analysis function. Hence, the features of this solutioninteract to enable an improved ability to detect mechanical wear ordamage in a machine having a part rotatable with a variable speed ofrotation.

BRIEF DESCRIPTION OF THE DRAWINGS

For simple understanding of the present invention, it will be describedby means of examples and with reference to the accompanying drawings, ofwhich:

FIG. 1 shows a schematic block diagram of an embodiment of a conditionanalyzing system 2 according to an embodiment of the invention.

FIG. 2A is a schematic block diagram of an embodiment of a part of thecondition analyzing system 2 shown in FIG. 1.

FIG. 3 is a simplified illustration of a Shock Pulse Measurement sensoraccording to an embodiment of the invention.

FIG. 4 is a simplified illustration of an embodiment of the memory 60and its contents.

FIG. 5 is a schematic block diagram of an embodiment of the analysisapparatus at a client location with a machine 6 having a movable shaft.

FIG. 6 illustrates a schematic block diagram of an embodiment of thepreprocessor according to an embodiment of the present invention.

FIG. 7 illustrates an embodiment of the evaluator 230.

FIG. 8 illustrates another embodiment of the evaluator 230.

FIG. 9 illustrates another embodiment of the pre-processor 200.

FIG. 10A is a flow chart that illustrates embodiments of a method forenhancing repetitive signal patterns in signals.

FIG. 10B is a flow chart illustrating a method of generating a digitaloutput signal.

FIG. 10C illustrates an embodiment of enhancer.

FIG. 10D illustrates signals according to an embodiment of the enhancermethod.

FIG. 10E illustrates an embodiment of a method of operating a userinterface of the enhancer.

FIG. 10F illustrates an embodiment of a method of operating theenhancer.

FIG. 10G illustrates another embodiment of enhancer 320.

FIG. 10H is a table for illustrating a part of the calculation of outputsignal values.

FIG. 11 is a schematic illustration of a first memory having pluralmemory positions

FIG. 12 is a schematic illustration of a second memory having pluralmemory positions t.

FIG. 13 is a schematic illustration of an example output signal S_(MDP)comprising two repetitive signals signatures.

FIG. 14A illustrates a number of sample values in the signal deliveredto the input of the decimator 310.

FIG. 14B illustrates output sample values of the corresponding timeperiod.

FIG. 15A illustrates a decimator according to an embodiment of theinvention.

FIG. 15B illustrates another embodiment of the invention.

FIG. 16 illustrates an embodiment of the invention including a decimatorand an enhancer, as described above, and a fractional decimator.

FIG. 17 illustrates an embodiment of the fractional decimator.

FIG. 18 illustrates another embodiment of the fractional decimator.

FIG. 19A illustrates decimator and another embodiment of fractionaldecimator.

FIG. 19B is a block diagram of an embodiment of a speed value generator601.

FIG. 19C is a simplified illustration of an embodiment of the memory 602and its contents.

FIG. 19D is a flow chart illustrating an embodiment of a method ofoperating the speed value generator 601 of FIG. 19B.

FIG. 19E is a flow chart illustrating an embodiment of a method forperforming step S#40 of FIG. 19D.

FIG. 19F is a flow chart illustrating another embodiment of a method forperforming step S#40 of FIG. 19D.

FIG. 19G is a graph illustrating a series of temporally consecutiveposition signals and advantageous effects of the method according to anembodiment of a speed value generator.

FIG. 20 is a block diagram of decimator and yet another embodiment offractional decimator.

FIG. 21 is a flow chart illustrating an embodiment of a method ofoperating the decimator and the fractional decimator of FIG. 20.

FIGS. 22A, 22B & 22C describe a method which may be implemented as acomputer program.

FIG. 23 is a front view illustrating an epicyclic gear system.

FIG. 24 is a schematic side view of the epicyclic gear system 700 ofFIG. 23, as seen in the direction of the arrow SW in FIG. 23.

FIG. 25 illustrates an analogue version of an exemplary signal producedby and outputted by the pre-processor 200 (see FIG. 5 or FIG. 16) inresponse to signals detected by the at least one sensor 10 upon rotationof the epicyclic gear system.

FIG. 26 illustrates an example of a portion of the high amplitude region702A of the signal shown in FIG. 25.

FIG. 27 illustrates an exemplary frequency spectrum of a signalcomprising a small periodic disturbance 903 as illustrated in FIG. 26.

FIG. 28 illustrates an example of a portion of the exemplary signalshown in FIG. 25.

FIG. 29 illustrates yet an embodiment of a condition analyzing systemaccording to an embodiment of the invention.

FIG. 30 is a block diagram illustrating the parts of the signalprocessing arrangement of FIG. 29 together with the user interface andthe display.

FIG. 31 is a schematic illustration of a parameter controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description similar features in different embodimentsmay be indicated by the same reference numerals.

FIG. 1 shows a schematic block diagram of an embodiment of a conditionanalyzing system 2 according to an embodiment of the invention.Reference numeral 4 relates to a client location with a machine 6 havinga movable part 8. The movable part may comprise bearings 7 and a shaft 8which, when the machine is in operation, rotates.

The operating condition of the shaft 8 or of a bearing 7 can bedetermined in response to vibrations emanating from the shaft and/orbearing when the shaft rotates. The client location 4, which may also bereferred to as client part or user part, may for example be the premisesof a wind farm, i.e. a group of wind turbines at a location, or thepremises of a paper mill plant, or some other manufacturing plant havingmachines with movable parts.

An embodiment of the condition analyzing system 2 is operative when asensor 10 is attached on or at a measuring point 12 on the body of themachine 6. Although FIG. 1 only illustrates two measuring points 12, itto be understood that a location 4 may comprise any number of measuringpoints 12. The condition analysis system 2 shown in FIG. 1, comprises ananalysis apparatus 14 for analysing the condition of a machine on thebasis of measurement values delivered by the sensor 10.

The analysis apparatus 14 has a communication port 16 for bi-directionaldata exchange. The communication port 16 is connectable to acommunications network 18, e.g. via a data interface 19. Thecommunications network 18 may be the world wide internet, also known asthe Internet. The communications network 18 may also comprise a publicswitched telephone network.

A server computer 20 is connected to the communications network 18. Theserver 20 may comprise a database 22, user input/output interfaces 24and data processing hardware 26, and a communications port 29. Theserver computer 20 is located on a location 28, which is geographicallyseparate from the client location 4. The server location 28 may be in afirst city, such as the Swedish capital Stockholm, and the clientlocation may be in another city, such as Stuttgart, Germany or Detroitin Michigan, USA. Alternatively, the server location 28 may be in afirst part of a town and the client location may be in another part ofthe same town. The server location 28 may also be referred to assupplier part 28, or supplier part location 28.

According to an embodiment of the invention a central control location31 comprises a control computer 33 having data processing hardware andsoftware for surveying a plurality of machines at the client location 4.The machines 6 may be wind turbines or gear boxes used in wind turbines.Alternatively the machines may include machinery in e.g. a paper mill.The control computer 33 may comprise a database 22B, user input/outputinterfaces 24B and data processing hardware 26B, and a communicationsport 29B. The central control location 31 may be separated from theclient location 4 by a geographic distance. By means of communicationsport 29B the control computer 33 can be coupled to communicate withanalysis apparatus 14 via port 16. The analysis apparatus 14 may delivermeasurement data being partly processed so as to allow further signalprocessing and/or analysis to be performed at the central location 31 bycontrol computer 33.

A supplier company occupies the supplier part location 28. The suppliercompany may sell and deliver analysis apparatuses 14 and/or software foruse in an analysis apparatus 14. The supplier company may also sell anddeliver analysis software for use in the control computer at the centralcontrol location 31. Such analysis software 94,105 is discussed inconnection with FIG. 4 below. Such analysis software 94,105 may bedelivered by transmission over said communications network 18.

According to one embodiment of the system 2 the apparatus 14 is aportable apparatus which may be connected to the communications network18 from time to time.

According to another embodiment of the system 2 the apparatus 14 maysubstantially continuously receive a measurement signal from a sensor 10so as to enable continuous or substantially continuous monitoring of themachine condition. The apparatus 14 according to this embodiment mayalso substantially continuously be capable of communicating with thecontrol computer 33 at control location 31. Hence, the apparatus 14according to this embodiment may substantially always be availableon-line for communication with the control computer 33 at controllocation 31.

According to an embodiment of the system 2 the apparatus 14 is connectedto the communications network 18 substantially continuously. Hence, theapparatus 14 according to this embodiment may substantially always be“on line” available for communication with the supplier computer 20and/or with the control computer 33 at control location 31.

FIG. 2A is a schematic block diagram of an embodiment of a part of thecondition analyzing system 2 shown in FIG. 1. The condition analyzingsystem, as illustrated in FIG. 2A, comprises a sensor unit 10 forproducing a measured value. The measured value may be dependent onmovement or, more precisely, dependent on vibrations or shock pulsescaused by bearings when the shaft rotates.

An embodiment of the condition analyzing system 2 is operative when adevice 30 is firmly mounted on or at a measuring point on a machine 6.The device 30 mounted at the measuring point may be referred to as astud 30. A stud 30 can comprise a connection coupling 32 to which thesensor unit 10 is removably attachable. The connection coupling 32 can,for example comprise double start threads for enabling the sensor unitto be mechanically engaged with the stud by means of a ¼ turn rotation.

A measuring point 12 can comprise a threaded recess in the casing of themachine. A stud 30 may have a protruding part with threads correspondingto those of the recess for enabling the stud to be firmly attached tothe measuring point by introduction into the recess like a bolt.

Alternatively, a measuring point can comprise a threaded recess in thecasing of the machine, and the sensor unit 10 may comprise correspondingthreads so that it can be directly introduced into the recess.Alternatively, the measuring point is marked on the casing of themachine only with a painted mark.

The machine 6 exemplified in FIG. 2A may have a rotating shaft with acertain shaft diameter dl. The shaft in the machine 24 may rotate with aspeed of rotation V1 when the machine 6 is in use.

The sensor unit 10 may be coupled to the apparatus 14 for analysing thecondition of a machine. With reference to FIG. 2A, the analysisapparatus 14 comprises a sensor interface 40 for receiving a measuredsignal or measurement data, produced by the sensor 10. The sensorinterface 40 is coupled to a data processing means 50 capable ofcontrolling the operation of the analysis apparatus 14 in accordancewith program code. The data processing means 50 is also coupled to amemory 60 for storing said program code.

According to an embodiment of the invention the sensor interface 40comprises an input 42 for receiving an analogue signal, the input 42being connected to an analogue-to-digital (A/D) converter 44, thedigital output 48 of which is coupled to the data processing means 50.The A/D converter 44 samples the received analogue signal with a certainsampling frequency f_(S) so as to deliver a digital measurement datasignal S_(MD) having said certain sampling frequency f_(S) and whereinthe amplitude of each sample depends on the amplitude of the receivedanalogue signal at the moment of sampling.

According to an embodiment of the invention the sensor is a Shock PulseMeasurement sensor. FIG. 3 is a simplified illustration of a Shock PulseMeasurement sensor 10 according to an embodiment of the invention.According to this embodiment the sensor comprises a part 110 having acertain mass or weight and a piezo-electrical element 120. Thepiezo-electrical element 120 is somewhat flexible so that it cancontract and expand when exerted to external force. The piezo-electricalelement 120 is provided with electrically conducting layers 130 and 140,respectively, on opposing surfaces. As the piezo-electrical element 120contracts and expands it generates an electric signal which is picked upby the conducting layers 130 and 140. Accordingly, a mechanicalvibration is transformed into an analogue electrical measurement signalS_(EA), which is delivered on output terminals 145, 150. Thepiezo-electrical element 120 may be positioned between the weight 110and a surface 160 which, during operation, is physically attached to themeasuring point 12, as illustrated in FIG. 3.

The Shock Pulse Measurement sensor 10 has a predetermined mechanicalresonance frequency that depends on the mechanical characteristics forthe sensor, such as the mass m of weight part 110 and the resilience ofpiezo-electrical element 120. Hence, the piezo-electrical element has anelasticity and a spring constant k. The mechanical resonance frequencyf_(RM) for the sensor is therefore also dependent on the mass m and thespring constant k.

According to an embodiment of the invention the mechanical resonancefrequency f_(RM) for the sensor can be determined by the equationfollowing equation:

f _(RM)=1/(2π)√(k/m)  (eq1)

According to another embodiment the actual mechanical resonancefrequency for a Shock Pulse Measurement sensor 10 may also depend onother factors, such as the nature of the attachment of the sensor 10 tothe body of the machine 6.

The resonant Shock Pulse Measurement sensor 10 is thereby particularlysensitive to vibrations having a frequency on or near the mechanicalresonance frequency f_(RM). The Shock Pulse Measurement sensor 10 may bedesigned so that the mechanical resonance frequency f_(RM) is somewherein the range from 28 kHz to 37 kHz. According to another embodiment themechanical resonance frequency f_(RM) is somewhere in the range from 30kHz to 35 kHz.

Accordingly the analogue electrical measurement signal has an electricalamplitude which may vary over the frequency spectrum. For the purpose ofdescribing the theoretical background, it may be assumed that if theShock Pulse Measurement sensor 10 were excelled to mechanical vibrationswith identical amplitude in all frequencies from e.g. 1 Hz to e.g. 200000 kHz, then the amplitude of the analogue signal S_(EA) from the ShockPulse Measurement Sensor will have a maximum at the mechanical resonancefrequency f_(RM), since the sensor will resonate when being “pushed”with that frequency.

The A/D converter 44 samples the received analogue signal S_(EA) with acertain sampling frequency f_(s) so as to deliver a digital measurementdata signal S_(MD) having said certain sampling frequency f_(s) andwherein the amplitude of each sample depends on the amplitude of thereceived analogue signal at the moment of sampling.

According to embodiments of the invention the digital measurement datasignal S_(MD) is delivered to a means 180 for digital signal processing(See FIG. 5).

According to an embodiment of the invention the means 180 for digitalsignal processing comprises the data processor 50 and program code forcausing the data processor 50 to perform digital signal processing.According to an embodiment of the invention the processor 50 is embodiedby a Digital Signal Processor. The Digital Signal Processor may also bereferred to as a DSP.

With reference to FIG. 2A, the data processing means 50 is coupled to amemory 60 for storing said program code. The program memory 60 ispreferably a nonvolatile memory. The memory 60 may be a read/writememory, i.e. enabling both reading data from the memory and writing newdata onto the memory 60. According to an embodiment the program memory60 is embodied by a FLASH memory. The program memory 60 may comprise afirst memory segment 70 for storing a first set of program code 80 whichis executable so as to control the analysis apparatus 14 to performbasic operations (FIG. 2A and FIG. 4). The program memory may alsocomprise a second memory segment 90 for storing a second set of programcode 94. The second set of program code 94 in the second memory segment90 may include program code for causing the analysis apparatus toprocess the detected signal, or signals, so as to generate apre-processed signal or a set of pre-processed signals. The memory 60may also include a third memory segment 100 for storing a third set ofprogram code 104. The set of program code 104 in the third memorysegment 100 may include program code for causing the analysis apparatusto perform a selected analysis function 105. When an analysis functionis executed it may cause the analysis apparatus to present acorresponding analysis result on user interface 106 or to deliver theanalysis result on port 16 (See FIG. 1 and FIG. 2A and FIGS. 7 and 8).

The data processing means 50 is also coupled to a read/write memory 52for data storage. Moreover, the data processing means 50 may be coupledto an analysis apparatus communications interface 54. The analysisapparatus communications interface 54 provides for bi-directionalcommunication with a measuring point communication interface 56 which isattachable on, at or in the vicinity of the measuring point on themachine.

The measuring point 12 may comprise a connection coupling 32, a readableand writeable information carrier 58, and a measuring pointcommunication interface 56.

The writeable information carrier 58, and the measuring pointcommunication interface 56 may be provided in a separate device 59placed in the vicinity of the stud 30, as illustrated in FIG. 2.Alternatively the writeable information carrier 58, and the measuringpoint communication interface 56 may be provided within the stud 30.This is described in more detail in WO 98/01831, the content of which ishereby incorporated by reference.

The system 2 is arranged to allow bidirectional communication betweenthe measuring point communication interface 56 and the analysisapparatus communication interface 54. The measuring point communicationinterface 56 and the analysis apparatus communication interface 54 arepreferably constructed to allow wireless communication. According to anembodiment the measuring point communication interface and the analysisapparatus communication interface are constructed to communicate withone another by radio frequency (RF) signals. This embodiment includes anantenna in the measuring point communication interface 56 and anotherantenna the analysis apparatus communication interface 54.

FIG. 4 is a simplified illustration of an embodiment of the memory 60and its contents. The simplified illustration is intended to conveyunderstanding of the general idea of storing different program functionsin memory 60, and it is not necessarily a correct technical teaching ofthe way in which a program would be stored in a real memory circuit. Thefirst memory segment 70 stores program code for controlling the analysisapparatus 14 to perform basic operations. Although the simplifiedillustration of FIG. 4 shows pseudo code, it is to be understood thatthe program code 80 may be constituted by machine code, or any levelprogram code that can be executed or interpreted by the data processingmeans 50 (FIG. 2A).

The second memory segment 90, illustrated in FIG. 4, stores a second setof program code 94. The program code 94 in segment 90, when run on thedata processing means 50, will cause the analysis apparatus 14 toperform a function, such as a digital signal processing function. Thefunction may comprise an advanced mathematical processing of the digitalmeasurement data signal S_(MD). According to embodiments of theinvention the program code 94 is adapted to cause the processor means 50to perform signal processing functions described in connection withFIGS. 5, 6, 9 and/or FIG. 16 in this document.

As mentioned above in connection with FIG. 1, a computer program forcontrolling the function of the analysis apparatus may be downloadedfrom the server computer 20. This means that theprogram-to-be-downloaded is transmitted to over the communicationsnetwork 18. This can be done by modulating a carrier wave to carry theprogram over the communications network 18. Accordingly the downloadedprogram may be loaded into a digital memory, such as memory 60 (SeeFIGS. 2A and 4). Hence, a signal processing program 94 and or ananalysis function program 104, 105 may be received via a communicationsport, such as port 16 (FIGS. 1 & 2A), so as to load it into memory 60.Similarly, a signal processing program 94 and or an analysis functionprogram 104, 105 may be received via communications port 29B (FIG. 1),so as to load it into a program memory location in computer 26B or indatabase 22B.

An aspect of the invention relates to a computer program product, suchas a program code means 94 and/or program code means 104, 105 loadableinto a digital memory of an apparatus. The computer program productcomprising software code portions for performing signal processingmethods and/or analysis functions when said product is run on a dataprocessing unit 50 of an apparatus for analysing the condition of amachine. The term “run on a data processing unit” means that thecomputer program plus the data processing unit carries out a method ofthe kind described in this document.

The wording “a computer program product, loadable into a digital memoryof a condition analysing apparatus” means that a computer program can beintroduced into a digital memory of a condition analysing apparatus soas achieve a condition analysing apparatus programmed to be capable of,or adapted to, carrying out a method of the kind described above. Theterm “loaded into a digital memory of a condition analysing apparatus”means that the condition analysing apparatus programmed in this way iscapable of, or adapted to, carrying out a method of the kind describedabove.

The above mentioned computer program product may also be loadable onto acomputer readable medium, such as a compact disc or DVD. Such a computerreadable medium may be used for delivery of the program to a client.

According to an embodiment of the analysis apparatus 14 (FIG. 2A), itcomprises a user input interface 102, whereby an operator may interactwith the analysis apparatus 14. According to an embodiment the userinput interface 102 comprises a set of buttons 104. An embodiment of theanalysis apparatus 14 comprises a user output interface 106. The useroutput interface may comprise a display unit 106. The data processingmeans 50, when it runs a basic program function provided in the basicprogram code 80, provides for user interaction by means of the userinput interface 102 and the display unit 106. The set of buttons 104 maybe limited to a few buttons, such as for example five buttons, asillustrated in FIG. 2A. A central button 107 may be used for an ENTER orSELECT function, whereas other, more peripheral buttons may be used formoving a cursor on the display 106. In this manner it is to beunderstood that symbols and text may be entered into the apparatus 14via the user interface. The display unit 106 may, for example, display anumber of symbols, such as the letters of alphabet, while the cursor ismovable on the display in response to user input so as to allow the userto input information.

FIG. 5 is a schematic block diagram of an embodiment of the analysisapparatus 14 at a client location 4 with a machine 6 having a movableshaft 8. The sensor 10, which may be a Shock Pulse Measurement Sensor,is shown attached to the body of the machine 6 so as to pick upmechanical vibrations and so as to deliver an analogue measurementsignal S_(EA) indicative of the detected mechanical vibrations to thesensor interface 40. The sensor interface 40 may be designed asdescribed in connection with FIG. 2A or 2B. The sensor interface 40delivers a digital measurement data signal S_(MD) to a means 180 fordigital signal processing.

The digital measurement data signal S_(MD) has a sampling frequencyf_(s), and the amplitude value of each sample depends on the amplitudeof the received analogue measurement signal S_(EA) at the moment ofsampling. According to an embodiment the sampling frequency f_(S) of thedigital measurement data signal S_(MD) may be fixed to a certain valuef_(S), such as e.g. f_(S)=102 400 Hz. The sampling frequency f_(S) maybe controlled by a clock signal delivered by a clock 190, as illustratedin FIG. 5. The clock signal may also be delivered to the means 180 fordigital signal processing. The means 180 for digital signal processingcan produce information about the temporal duration of the receiveddigital measurement data signal S_(MD) in response to the receiveddigital measurement data signal S1vm, the clock signal and the relationbetween the sampling frequency f_(S) and the clock signal, since theduration between two consecutive sample values equals Ts=1/f_(S).

According to embodiments of the invention the means 180 for digitalsignal processing includes a pre-processor 200 for performing apre-processing of the digital measurement data signal S_(MD) so as todeliver a pre-processed digital signal S_(MDP) on an output 210. Theoutput 210 is coupled to an input 220 of an evaluator 230. The evaluator230 is adapted to evaluate the pre-processed digital signal S_(MDP) soas to deliver a result of the evaluation to a user interface 106.Alternatively the result of the evaluation may be delivered to acommunication port 16 so as to enable the transmission of the resulte.g. to a control computer 33 at a control site 31 (See FIG. 1).

According to an embodiment of the invention, the functions described inconnection with the functional blocks in means 180 for digital signalprocessing, pre-processor 200 and evaluator 230 may be embodied bycomputer program code 94 and/or 104 as described in connection withmemory blocks 90 and 100 in connection with FIG. 4 above.

A user may require only a few basic monitoring functions for detectionof whether the condition of a machine is normal or abnormal. Ondetecting an abnormal condition, the user may call for specializedprofessional maintenance personnel to establish the exact nature of theproblem, and for performing the necessary maintenance work. Theprofessional maintenance personnel frequently needs and uses a broadrange of evaluation functions making it possible to establish the natureof, and/or cause for, an abnormal machine condition. Hence, differentusers of an analysis apparatus 14 may pose very different demands on thefunction of the apparatus. The term Condition Monitoring function isused in this document for a function for detection of whether thecondition of a machine is normal or somewhat deteriorated or abnormal.The term Condition Monitoring function also comprises an evaluationfunction making it possible to establish the nature of, and/or causefor, an abnormal machine condition.

Examples of Machine Condition Monitoring Functions

The condition monitoring functions F1, F2 . . . Fn includes functionssuch as: vibration analysis, temperature analysis, shock pulsemeasuring, spectrum analysis of shock pulse measurement data, FastFourier Transformation of vibration measurement data, graphicalpresentation of condition data on a user interface, storage of conditiondata in a writeable information carrier on said machine, storage ofcondition data in a writeable information carrier in said apparatus,tachometering, imbalance detection, and misalignment detection.

According to an embodiment the apparatus 14 includes the followingfunctions:

-   -   F1=vibration analysis:    -   F2=temperature analysis,    -   F3=shock pulse measuring,    -   F4=spectrum analysis of shock pulse measurement data,    -   F5=Fast Fourier Transformation of vibration measurement data,    -   F6=graphical presentation of condition data on a user interface,    -   F7=storage of condition data in a writeable information carrier        on said machine,    -   F8=storage of condition data in a writeable information carrier        52 in said apparatus,    -   F9=tachometering,    -   F10=imbalance detection, and    -   F1l=misalignment detection.    -   F12=Retrieval of condition data from a writeable information        carrier 58 on said machine.    -   F13=Performing vibration analysis function F1 and performing        function F12 “Retrieval of condition data from a writeable        information carrier 58 on said machine” so as to enable a        comparison or trending based on current vibration measurement        data and historical vibration measurement data.    -   F14=Performing temperature analysis F2; and performing function        “Retrieval of condition data from a writeable information        carrier 58 on said machine” so as to enable a comparison or        trending based on current temperature measurement data and        historical temperature measurement data.    -   F15=Retrieval of identification data from a writeable        information carrier 58 on said machine.

Embodiments of the function F7 “storage of condition data in a writeableinformation carrier on said machine”, and F13 vibration analysis andretrieval of condition data is described in more detail in WO 98/01831,the content of which is hereby incorporated by reference.

FIG. 6 illustrates a schematic block diagram of an embodiment of thepre-processor 200 according to an embodiment of the present invention.In this embodiment the digital measurement data signal S_(MD) is coupledto a digital band pass filter 240 having a lower cutoff frequencyf_(LC), an upper cutoff frequency f_(UC) and passband bandwidth betweenthe upper and lower cutoff frequencies.

The output from the digital band pass filter 240 is connected to adigital enveloper 250. According to an embodiment of the invention thesignal output from the enveloper 250 is delivered to an output 260. Theoutput 260 of the pre-processor 200 is coupled to output 210 of digitalsignal processing means 180 for delivery to the input 220 of evaluator230.

The upper and lower cutoff frequencies of the digital band pass filter240 may selected so that the frequency components of the signal S_(MD)at the resonance frequency f_(RM) for the sensor are in the passbandbandwidth. As mentioned above, an amplification of the mechanicalvibration is achieved by the sensor being mechanically resonant at theresonance frequency f_(RM). Accordingly the analogue measurement signalS_(EA) reflects an amplified value of the vibrations at and around theresonance frequency f_(RM). Hence, the band pass filter according to theFIG. 6 embodiment advantageously suppresses the signal at frequenciesbelow and above resonance frequency f_(RM), so as to further enhance thecomponents of the measurement signal at the resonance frequency f_(RM).Moreover, the digital band pass filter 240 advantageously furtherreduces noise inherently included in the measurement signal, since anynoise components below the lower cutoff frequency f_(LC), and aboveupper cutoff frequency f_(UC) are also eliminated or reduced. Hence,when using a resonant Shock Pulse Measurement sensor 10 having amechanical resonance frequency f_(RM) in a range from a lowest resonancefrequency value f_(RML) to a highest resonance frequency value f_(RMU)the digital band pass filter 240 may be designed to having a lowercutoff frequency f_(LC)=f_(RML), and an upper cutoff frequencyf_(UC)=f_(RMU). According to an embodiment the lower cutoff frequencyf_(LC)=f_(RML)=28 kHz, and the upper cutoff frequency f_(UC)=f_(RMU)=37kHz.

According to another embodiment the mechanical resonance frequencyf_(RM) is somewhere in the range from 30 kHz to 35 kHz, and the digitalband pass filter 240 may then be designed to having a lower cutofffrequency f_(LC)=30 kHz and an upper cutoff frequency f_(UC)=35 kHz.

According to another embodiment the digital band pass filter 240 may bedesigned to have a lower cutoff frequency f_(LC) being lower than thelowest resonance frequency value f_(RM), and an upper cutoff frequencyf_(UC) being higher than the highest resonance frequency value f_(RMU).For example the mechanical resonance frequency f_(RM) may be a frequencyin the range from 30 kHz to 35 kHz, and the digital band pass filter 240may then be designed to having a lower cutoff frequency f_(LC)=17 kHz,and an upper cutoff frequency f_(UC)=36 kHz.

Accordingly, the digital band pass filter 240 delivers a passbanddigital measurement data signal SF having an advantageously low noisecontent and reflecting mechanical vibrations in the passband. Thepassband digital measurement data signal SF is delivered to enveloper250.

The digital enveloper 250 accordingly receives the passband digitalmeasurement data signal SF which may reflect a signal having positive aswell as negative amplitudes. With reference to FIG. 6, the receivedsignal is rectified by a digital rectifier 270, and the rectified signalmay be filtered by an optional low pass filter 280 so as to produce adigital envelop signal S_(ENV).

Accordingly, the signal S_(ENV) is a digital representation of anenvelope signal being produced in response to the filtered measurementdata signal SF. According to some embodiments of the invention theoptional low pass filter 280 may be eliminated. One such embodiment isdiscussed in connection with FIG. 9 below. Accordingly, the optional lowpass filter 280 in enveloper 250 may be eliminated when decimator 310,discussed in connection with FIG. 9 below, includes a low pass filterfunction.

According to the FIG. 6 embodiment of the invention the signal S_(ENV)is delivered to the output 260 of pre-processor 200. Hence, according toan embodiment of the invention the pre-processed digital signal S_(MDP)delivered on the output 210 (FIG. 5) is the digital envelop signalS_(ENV).

Whereas prior art analogue devices for generating an envelope signal inresponse to a measurement signal employs an analogue rectifier whichinherently leads to a biasing error being introduced in the resultingsignal, the digital enveloper 250 will advantageously produce a truerectification without any biasing errors. Accordingly, the digitalenvelop signal S_(ENV) will have a good Signal-to-Noise Ratio, since thesensor being mechanically resonant at the resonance frequency in thepassband of the digital band pass filter 240 leads to a high signalamplitude and the signal processing being performed in the digitaldomain eliminates addition of noise and eliminates addition of biasingerrors.

With reference to FIG. 5 the pre-processed digital signal S_(MDP) isdelivered to input 220 of the evaluator 230.

According to another embodiment, the filter 240 is a high pass filterhaving a cut-off frequency f_(LC). This embodiment simplifies the designby replacing the band-pass filter with a high-pass filter 240, therebyleaving the low pass filtering to another low pass filter downstream,such as the low pass filter 280. The cut-off frequency f_(LC) of thehigh pass filter 240 is selected to approximately the value of thelowest expected mechanical resonance frequency value f_(RMU) of theresonant Shock Pulse Measurement sensor 10. When the mechanicalresonance frequency f_(RM) is somewhere in the range from 30 kHz to 35kHz, the high pass filter 240 may be designed to having a lower cutofffrequency f_(LC)=30 kHz. The high-pass filtered signal is then passed tothe rectifier 270 and on to the low pass filter 280.

According to an embodiment it should be possible to use sensors 10having a resonance frequency somewhere in the range from 20 kHz to 35kHz. In order to achieve this, the high pass filter 240 may be designedto having a lower cutoff frequency f_(LC)=20 kHz.

FIG. 7 illustrates an embodiment of the evaluator 230 (See also FIG. 5).The FIG. 7 embodiment of the evaluator 230 includes a condition analyser290 adapted to receive a pre-processed digital signal S_(MDP) indicativeof the condition of the machine 6. The condition analyser 290 can becontrolled to perform a selected condition analysis function by means ofa selection signal delivered on a control input 300. The selectionsignal delivered on control input 300 may be generated by means of userinteraction with the user interface 102 (See FIG. 2A). When the selectedanalysis function includes Fast Fourier Transform, the analyzer 290 willbe set by the selection signal 300 to operate on an input signal in thefrequency domain.

Dependent on what type of analysis to be performed the conditionanalyser 290 may operate on an input pre-processed digital signalS_(MDP) in the time domain, or on an input pre-processed digital signalS_(MDP) in the frequency domain. Accordingly, dependent on the selectionsignal delivered on control input 300, the FFT 294 may be included asshown in FIG. 8, or the signal S_(MDP) may be delivered directly to theanalyser 290 as illustrated in FIG. 7.

FIG. 8 illustrates another embodiment of the evaluator 230. In the FIG.8 embodiment the evaluator 230 includes an optional Fast FourierTransformer 294 coupled to receive the signal from input 220 of theevaluator 230. The output from the FFTransformer 294 may be delivered toanalyser 290.

In order to analyze the condition of a rotating part it is desired tomonitor the detected vibrations for a sufficiently long time to be ableto detect repetitive signals. Certain repetitive signal signatures areindicative of a deteriorated condition of the rotating part. An analysisof a repetitive signal signature may also be indicative of the type ofdeteriorated condition. Such an analysis may also result in detection ofthe degree of deteliorated condition.

Hence, the measurement signal may include at least one vibration signalcomponent SD dependent on a vibration movement of the rotationallymovable part 8; wherein said vibration signal component has a repetitionfrequency f_(D) which depends on the speed of rotation f_(ROT) of therotationally movable part 8. The vibration signal component which isdependent on the vibration movement of the rotationally movable part 8may therefore be indicative of a deteriorated condition or a damage ofthe monitored machine. In fact, a relation between repetition frequencyf_(D) of the vibration signal component Sn and the speed of rotationf_(ROT) of the rotationally movable part 8 may be indicative of whichmechanical part it is that has a damage. Hence, in a machine having aplurality of rotating parts it may be possible to identify an individualslightly damaged part by means of processing the measurement signalusing an analysis function 105, including a frequency analysis.

Such a frequency analysis may include fast fourier transformation of themeasurement signal including vibration signal component Sn. The fastfourier transformation (FFT), uses a certain frequency resolution. Thatcertain frequency resolution, which may he expressed in terms offrequency bins, determines the limit for discending differentfrequencies. The term “frequency bins” is sometimes referred to as“lines”. If a frequency resolution providing Z frequency bins up to theshaft speed is desired, then it is necessary to record the signal duringX revolutions of the shaft.

In connection with the analysis of rotation parts it may be interestingto analyse signal frequencies that are higher than the rotationfrequency f_(ROT) of the rotating part. The rotating part may include ashaft and hearings. The shaft rotation frequency f_(ROT) is oftenreferred to as “order 1”. The interesting bearing signals may occurabout ten times per shaft revolution (Order 10), i.e. a damagerepetition frequency f_(D) (measured in Hz) divided by rotational speedf_(ROT) (measured in rps) equals 10 Hz/rps, i.e. ordery=f_(D)/f_(ROT)=10 Hz/rps. Moreover, it may be interesting to analyseovertones of the bearing signals, so it may be interesting to measure upto order 100. Referring to a maximum order as Y, and the total number offrequency bins in the FFT to be used as Z, the following applies: Z=X*Y.Conversely, X=Z/Y, wherein

-   -   X is the number of revolutions of the monitored shaft during        which the digital signal is analysed; and    -   Y is a maximum order; and    -   Z is the frequency resolution expressed as a number of frequency        bins

Consider a case when the decimated digital measurement signal S_(MDP)(See FIG. 5) is delivered to the FFT analyzer 294, as described in FIG.8: In such a case, when the FFT analyzer 294 is set for Z=1600 frequencybins, and the user is interested in analysing frequencies up to orderY=100, then the value for X becomes X=Z/Y=1600/100=16.

Hence, it is necessary to measure during X=16 shaft revolutions whenZ=1600 frequency bins is desired and the user is interested in analysingfrequencies up to order Y=100.

The frequency resolution Z of the FFT analyzer 294 may be settable usingthe user interface 102, 106 (FIG. 2A).

Hence, the frequency resolution value Z for the condition analysisfunction 105 and/or signal processing function 94 (FIG. 4) may besettable using the user interface 102, 106 (FIG. 2A).

According to an embodiment of the invention, the frequency resolution Zis settable by selecting one value Z from a group of values. The groupof selectable values for the frequency resolution Z may include

Z=400

Z=800

Z=1600

Z=3200

Z=6400

As mentioned above, the sampling frequency f_(s) may be fixed to acertain value such as e.g f_(s)=102 400 kHz, and the factor k may be setto 2,56, thereby rendering the maximum frequency to be analyzedf_(SEAmax) to be:

f _(SEAmax) =f _(s) /k=102 400/2,56=40 kHz

For a machine having a shaft with rotational speed f_(ROT)=1715rpm=28,58 rps, a selected order value Y=100 renders a maximum frequencyto be analyzed to be

f _(ROT) *Y=28,58 rps*100=2858 Hz.

The FFTransformer 294 may be adapted to perform Fast Fourier Transformon a received input signal having a certain number of sample values. Itis advantageous when the certain number of sample values is set to aneven integer which may be divided by two (2) without rendering afractional number.

Accordingly, a data signal representing mechanical vibrations emanatingfrom rotation of a shaft may include repetitive signal patterns. Acertain signal pattern may thus be repeated a certain number of timesper revolution of the shaft being monitored. Moreover, repetitivesignals may occur with mutually different repetition frequency.

In the book “Machinery Vibration Measurements and Analysis” by VictorWowk (ISBN 0-07-071936-5), there is provided a couple of examples ofmutually different repetition frequencies on page 149:

“Fundamental train frequency (FTF)

Ball spin (BS) frequency

Outer Race (OR)

Inner Race (IR)”

The book also provides formulas for calculating these specificfrequencies on page 150. The content of the book “Machinery VibrationMeasurements and Analysis” by Victor Wowk, is hereby incorporated byreference. In particular the above mentioned formulas for calculatingthese specific frequencies are hereby incorporated by reference. A tableon page 151 of the same book indicates that these frequencies also varydependent on bearing manufacturer, and that

FTF may have a bearing frequency factor of 0,378;

BS may have a bearing frequency factor of 1,928;

OR may have a bearing frequency factor of 3,024; and

IR may have a bearing frequency factor of 4,976

The frequency factor is multiplied with the rotational speed of theshaft to obtain the repetition frequency. The book indicates that for ashaft having a rotational speed of 1715 rpm, i.e. 28.58 Hz, therepetition frequency for a pulse emanating from the Outer Race (OR) of abearing of standard type 6311 may be about 86 Hz; and the FTF repetitionfrequency may be 10.8 Hz.

When the monitored shaft rotates at a constant rotational speed such arepetition frequency may be discussed either in terms of repetition pertime unit or in terms of repetition per revolution of the shaft beingmonitored, without distinguishing between the two. However, if themachine part rotates at a variable rotational speed the matter isfurther complicated, as discussed below in connection with FIGS. 16, 17and 20.

Machinely Presenting Sudden Damages

Some types of machinery may suffer complete machine failure or breakdownvery abruptly. For some machine types, such as rotating parts in a windpower station, breakdown has been known to occur suddenly and as acomplete surprise to the maintenance personnel and to the machine owner.Such sudden breakdown causes a lot of costs to the machine owner and maycause other negative side effects e.g. if machine parts fall off as aresult of unexpected mechanical failure. The inventor realized thatthere is a particularly high noise level in the mechanical vibrations ofcertain machinery, and that such noise levels hamper the detection ofmachine damages. Hence, for some types of machinery, conventionalmethods for preventive condition monitoring have failed to providesufficiently early and/or reliable warning of on-coming deterioratingconditions. The inventor concluded that there may exist a mechanicalvibration V_(MD) indicative of a deteriorated condition in suchmachinery, but that conventional methods for measuring vibrations mayhitherto have been inadequate.

The inventor realized that machines having slowly rotating parts wereamong the types of machinery that seem to be particularly prone tosudden failure. The inventor also realized that a low rotational speedf_(ROT) may lead to lower amplitudes of the mechanical vibration V_(MD).When the mechanical vibration V_(MD) indicative of an incipient machinedamage has a low amplitude, the noise content in the measuring signalwill become higher in relative terms. When measuring on a machine havingrotational speed of less than 50 rpm the enveloped and decimated digitalmeasurement signal S_(RED) delivered by the decimator 310 may be sonoisy as to prevent successful condition monitoring analysis if thedecimated digital measurement signal S_(RED) is fed directly to theanalyzer 290. In other words, the signal-to-noise ratio, SNR ofdecimated digital measurement signal S_(RED) may be so low as to preventthe detection of any vibration signal component SD.

Having realized that a particularly high noise level in the mechanicalvibrations of certain machinery hampers the detection of machinedamages, the inventor came up with a method for enabling detection ofweak mechanical signals in a noisy environment. As mentioned above, therepetition frequency f_(D) of vibration signal component SD in a noisymeasuring signal S_(EA) depends on a mechanical vibration V_(MD) whichis indicative of an incipient damage of a rotational part 8 of themonitored machine 6. The inventor realized that it may be possible todetect an incipient damage, i.e. a damage that is just starting todevelop, if a corresponding weak signal can be discerned.

Hence, the measurement signal may include at least one vibration signalcomponent SD dependent on a vibration movement of the rotationallymovable part 8; wherein said vibration signal component has a repetitionfrequency f_(D) which depends on the speed of rotation f_(ROT) of therotationally movable part 8. The existence of a vibration signalcomponent which is dependent on the vibration movement of therotationally movable part 8 may therefore provide an early indication ofa deteriorating condition or an incipient damage of the monitoredmachine.

In a wind turbine application the shaft whose bearing is analyzed mayrotate at a speed of less than 120 revolutions per minute, i.e. theshaft rotational frequency f_(ROT) is less than 2 revolutions per second(rps). Sometimes such a shaft to be analyzed rotates at a speed of lessthan 50 revolutions per minute (rpm), i.e. a shaft rotational frequencyf_(ROT) of less than 0,83 rps. In fact the speed of rotation maytypically be less than 15 rpm. Whereas a shaft having a rotational speedof 1715 rpm, as discussed in the above mentioned book, produces 500revolutions in just 17.5 seconds; a shaft rotating at 50 revolutions perminute takes ten minutes to produce 500 revolutions. Certain large windpower stations have shafts that may typically rotate at 12 RPM=0,2 rps.

Accordingly, when a bearing to be analyzed is associated with a slowlyrotating shaft, and the bearing is monitored by a detector generating ananalogue measurement signal S_(EA) which is sampled using a samplingfrequency f_(s) of about 100 kHz, the number of sampled valuesassociated with one full revolution of the shaft becomes very large. Asan illustrative example, it takes 60 million (60 000 000) sample valuesat a sampling frequency of 100 kHz to describe 500 revolutions when theshaft rotates at 50 rpm.

Moreover, performing advanced mathematical analysis of the signalrequires a lot of time when the signal includes so many samples.Accordingly it is desired to reduce the number of samples per secondbefore further processing of the signal S_(ENV).

FIG. 9 illustrates another embodiment of the pre-processor 200. The FIG.9 embodiment of the pre-processor 200 includes a digital band passfilter 240 and a digital enveloper 250 as described above in connectionwith FIG. 6. As mentioned above, the signal S_(ENV) is a digitalrepresentation of an enveloped signal which is produced in response tothe filtered measurement data signal SF.

According to the FIG. 9 embodiment of the pre-processor 200, the digitalenveloped signal S_(ENV) is delivered to a decimator 310 adapted toproduce a digital signal S_(RED) having a reduced sampling frequencyf_(SR1). The decimator 310 operates to produce an output digital signalwherein the temporal duration between two consecutive sample values islonger than the temporal duration between two consecutive sample valuesin the input signal. The decimator is described in more detail inconnection with FIG. 14, below. According to an embodiment of theinvention the optional low pass filter 280 may be eliminated, asmentioned above. When, in the FIG. 9 embodiment, the signal produced bythe digital rectifier 270 is delivered to decimator 310, which includeslow pass filtering, the low pass filter 280 may be eliminated.

An output 312 of the decimator 310 delivers the digital signal S_(RED)to an input 315 of an enhancer 320. The enhancer 320 is capable ofreceiving the digital signal S_(RED) and in response thereto generatingan output signal S_(MDP). The output signal S_(MDP) is delivered tooutput port 260 of pre-processor 200.

FIG. 10A is a flow chart that illustrates embodiments of a method forenhancing repetitive signal patterns in signals. This method mayadvantageously be used for enhancing repetitive signal patterns insignals representing the condition of a machine having a rotating shaft.An enhancer 320 may be designed to operate according to the methodillustrated by FIG. 10A.

Method steps S1000 to S1040 in FIG. 10A represent preparatory actions tobe taken in order to make settings before actually generating the outputsignal values.

When the preparatory actions have been executed, the output signalvalues may be calculated, as described with reference to step S1050.

FIG. 10B is a flow chart illustrating a method of generating a digitaloutput signal. More particularly, FIG. 10B illustrates an embodiment ofa method to generate a digital output signal when preparatory actionsdescribed with reference to steps S1000 to S1040 in FIG. 10A have beenperformed.

With reference to step S1000 in FIG. 10A, a desired length O_(LENGTH) ofan output signal S_(MDP) is determined.

FIG. 11 is a schematic illustration of a first memory having pluralmemory positions i. The memory positions i of the first memory hold anexample input signal I comprising a sequence of digital values. Theexample input signal is used for calculating the output signal S_(MDP)according to embodiments of the invention. FIG. 11 shows some of manyconsecutive digital values for the input signal I. The digital values2080 in the input signal I only illustrate a few of the digital valuesthat are present in the input signal. In FIG. 11 two neighbouringdigital values in the input signal are separated by a durationt_(delta). The value t_(delta) is the inverse of a sampling frequencyf_(SR) of the input signal received by the enhancer 320 (See FIG. 9 &FIG. 16).

FIG. 12 is a schematic illustration of a second memory having pluralmemory positions t. The memory positions t of the second memory hold anexample output signal S_(MDP) comprising a sequence of digital values.Hence, FIG. 12 illustrates a portion of a memory having digital values3090 stored in consecutive memory positions. FIG. 12 shows consecutivedigital values for the output signal S_(MDP). The digital values 3090 inthe output signal S_(MDP) only illustrate a few of the digital valuesthat are present in the output signal. In FIG. 12 two neighbouringdigital values in the output signal may be temporally separated by theduration t_(delta).

According to an embodiment, the user may input a value representing alowest repetition frequency f_(REPmin) to be detected as well asinformation about a lowest expected speed of rotation of the shaft to bemonitored. The analysis system 2 (FIG. 1) includes functionality forcalculating a suitable value for the variable O_(LENGTH) in response tothese values.

Alternatively, with reference to FIG. 2A, a user of an analysisapparatus 14 may set the value O_(LENGTH) 3010 of the output signalS_(MDP) by means of inputting a corresponding value via the userinterface 102.

In a next step S1010 a length factor L is chosen. The length factor Ldetermines how well stochastic signals are suppressed in the outputsignal S_(MDP). A higher value of L gives less stochastic signals in theoutput signal S_(MDP) than a lower value of L.

Hence, the length factor L may be referred to as a Signal-Noise Ratioimprover value, also referred to as SNR improver value. According to oneembodiment of the method L is an integer between 1 and 10, but L canalso be set to other values.

According to an embodiment of the method, the value L can be preset inthe enhancer 320. According to another embodiment of the method thevalue L is inputted by a user of the method through the user interface102 (FIG. 2A). The value of the factor L also has an impact oncalculation time required to calculate the output signal. A larger valueof L requires longer calculation time than a lower value of L.

Next, in a step S1020, a starting position S_(START) is set. Thestarting position S_(START) may indicate a position in the input signalI.

The starting position S_(START) is set to avoid or reduce the occurrenceof non-repetitive patterns in the output signal S_(MDP). When thestarting position S_(START) is set so that a part 2070 of the inputsignal before the starting position has a length which corresponds to acertain time interval T_(STOCHASTIC_MAX) then stochastic signals withthe a corresponding frequency f_(STOCHASTIC_MAX) and higher frequencieswill be attenuated in the output signal O, S_(MDP).

In a next step S1030 the required length of the input data signal iscalculated. The required length of the input data signal is calculatedin the step S1030 according to formula (1) below:

I _(LENGTH) =O _(LENGTH) *L+S _(START) +O _(LENGTH)  (1)

Next, in a step S1040, a length C_(LENGTH) in the input data signal iscalculated. The length C_(LENGTH) is the length over which thecalculation of the output data signal is performed. This lengthC_(LENGTH) is calculated according to formula (3) below.

C _(LENGTH) =I _(LENGTH) −S _(START) −O _(LENGTH)  (3)

Formula (3) can also be written asI_(LENGTH)=C_(LENGTH)+S_(START)+O_(LENGTH)

The output signal is then calculated in a step S1050. The output signalis calculated according to formula (5) below. In formula (5) a value forthe output signal is calculated for a time value tin the output signal.

$\begin{matrix}{{S_{MDP}(t)} = {{\sum\limits_{i = 1}^{i = {CLENGTH}}\; {{I(i)}^{*}{I\left( {i + S_{start} +} \right)}\mspace{14mu} {where}\mspace{14mu} 1}} \leq O_{LENGTH}}} & (5)\end{matrix}$

The output signal S_(MDP) has a length O_(LENGTH), as mentioned above.To acquire the entire output signal S_(MDP) a value for each time valuefrom t=1 to t=O_(LENGTH) has to be calculated with formula (5). In FIG.11 a digital value 2081 illustrates one digital value that is used inthe calculation of the output signal. The digital value 2081 illustratesone digital value that is used in the calculation of the output signalwhere i=1. The digital value 2082 illustrates another digital value thatis used in the calculation of the output signal. Reference numeral 2082refers to the digital value I(1+S_(START)+t) in formula (5) above, wheni=1 and t=1. Hence, reference numeral 2082 illustrates the digitalsample value at position number P in the input signal:

P=1+S _(START)+1=S _(START)+2.

In FIG. 12, reference numeral 3091 refers to the digital sample valueS_(MDP)(t) in the output signal where t=1.

Another embodiment of the method for operating the enhancer 320 forenhancing repetitive patterns in signals representing the condition of amachine having a rotating shaft will now be described. According to anembodiment the length O_(LENGTH) may be preset in the enhancer 320.According to other embodiments of the method the length O_(LENGTH) maybe set by user input through the user interface 102 (FIG. 2A). Accordingto a preferred embodiment of the method the variable O_(LENGTH) is setto an even integer which may be divided by two (2) without rendering afractional number. Selecting the variable O_(LENGTH) according to thisrule advantageously adapts the number of samples in the output signal sothat it is suitable for use in the optional Fast Fourier Transformer294. Hence, according to embodiments of the method the variableO_(LENGTH) may preferably be set to a number such as e.g. 1024, 2048,4096.

In a particularly advantageous embodiment the value S_(START) is set, instep S1020, so that the part 2070 of the input signal before thestarting position has the same length as the output signal 3040, i.e.S_(START)=O_(LENGTH).

As mentioned in connection with equation (1) above, the required lengthof the input data signal is

I _(LENGTH) =O _(LENGTH) *L+S _(START) +O _(LENGTH)

Hence, setting S_(START)=O_(LENGTH) in eq (1) renders

I _(LENGTH) =O _(LENGTH) *L+O _(LENGTH) +O _(LENGTH) =O _(LENGTH) *L+O_(LENGTH)*2

Accordingly, the required length of the input signal can be expressed interms of the length of the output signal according to equation (6)below.

I _(LENGTH)=(L+2)*O _(LENGTH)  (6)

where L is the length factor discussed above, and O_(LENGTH) is thenumber of digital values in the output signal, as discussed above.

The length C_(LENGTH) can be calculated, in this embodiment of theinvention, according to formula (7) below.

C _(LENGTH) =L*O _(LENGTH)  (7)

When the preparatory actions described with reference to steps S1000 toS1040 in FIG. 10A have been performed, the digital output signal may begenerated by means of a method as described with reference to FIG. 10B.According to an embodiment of the invention, the method described withreference to FIG. 10B is performed by means of a DSP 50 (FIG. 2A).

In a step S1100 (FIG. 10B) the enhancer 320 receives a digital inputsignal I having a first plurality I_(LENGTH) of sample values on aninput 315 (See FIG. 9 and/or FIG. 16). As noted above the digital inputsignal I may represent mechanical vibrations emanating from rotation ofa shaft so far as to cause occurrence of a vibration having a period ofrepetition TR.

The received signal values are stored (Step S1120) in an input signalstorage portion of a data memory associated with the enhancer 320.According to an embodiment of the invention the data memory may beembodied by the read/write memory 52 (FIG. 2A).

In a step S1130 the variable t, used in equation (5) above, is set to aninitial value. The initial value may be 1 (one).

In step S1140 an output sample value S_(MDP)(t) is calculated for samplenumber t. The calculation may employ the below equation:

${{s_{MDP}(t)} = {\sum\limits_{i = 1}^{i = {CLENGTH}}\; {{I(i)}^{*}{I\left( {i + {Sstart} + t} \right)}}}}\mspace{14mu}$

The resulting sample value S_(MDP)(t) is stored (Step S1150, FIG. 10B)in an output signal storage portion of the memory 52 (See FIG. 12).

In a step S1160 the process checks the value of variable t, and if thevalue of t represents a number lower than the desired number of outputsample values O_(LENGTH) a step S1160 is performed for increasing thevalue of variable t, before repeating steps S1140, S1150 and S1160.

If, in step S1160, the value oft represents a number equal to thedesired number of output sample values O_(LENGTH) a step S1180 isperformed.

In step S1180 the output signal O, S_(MDP) is delivered on output 260(See FIG. 9 and/or FIG. 16).

As mentioned above, a data signal representing mechanical vibrationsemanating from rotation of a shaft may include repetitive signalsignatures, and a certain signal signature may thus be repeated acertain number of times per revolution of the shaft being monitored.Moreover, several mutually different repetitive signal signatures mayoccur, wherein the mutually different repetitive signal signatures mayhave mutually different repetition frequency. The method for enhancingrepetitive signal signatures in signals, as described above,advantageously enables simultaneous detection of many repetitive signalsignatures having mutually different repetition frequency. Thisadvantageously enables the simultaneous detection of e.g a Bearing InnerRace damage signature and a Bearing Outer Race damage signature in asingle measuring and analysis session, as described below.

FIG. 13 is a schematic illustration of an example output signal S_(MDP)comprising two repetitive signals signatures 4010 and 4020. The outputsignal S_(MDP) may comprise more repetitive signals signatures than theones illustrated in FIG. 13, but for illustrative purpose only tworepetitive signal signatures are shown. Only some of many digital valuesfor the repetitive signals signatures 4010 and 4020 are shown in FIG.13.

In FIG. 13 the Outer Race (OR) frequency signal 4020 and the Inner Race(IR) frequency signal 4010 are illustrated. As can be seen in FIG. 13the Outer Race (OR) frequency signal 4020 has a lower frequency than theInner Race (IR) frequency signal 4010. The repetition frequency for theOuter Race (OR) frequency signal 4020 and the Inner Race (IR) frequencysignal 4010 is 1/T_(OR) and 1/T_(IR), respectively.

In the above described embodiments of the method of operating theenhancer 320 for enhancing repetitive signal patterns the repetitivesignal patterns are amplified when calculating the output signal in stepS1050. A higher amplification of the repetitive signal patterns isachieved if the factor L is given a higher value, in step S1010, than ifL is given a lower value. A higher value of L means that a longer inputsignal I_(LENGTH) is required in step S1030. A longer input signalI_(LENGTH) therefore results in a higher amplification of the repetitivesignal patterns in the output signal. Hence, a longer input signalI_(LENGTH) renders the effect of better attenuation of stochasticsignals in relation to the repetitive signal patterns in the outputsignal.

According to an embodiment of the invention the integer value I_(LENGTH)may be selected in response to a desired amount of attenuation ofstochastic signals. In such an embodiment the length factor L may bedetermined in dependence on the selected integer value I_(LENGTH).

Now consider an exemplary embodiment of the method for operating theenhancer 320 for enhancing repetitive signal patterns where the methodis used for amplification of a repetitive signal pattern with a certainlowest frequency. In order to be able to analyse the repetitive signalpattern with the certain lowest frequency a certain length of the outputsignal is required.

As mentioned above, using a longer input data signal in the calculationof the output signal results in that the repetitive signal pattern isamplified more than if a shorter input data signal is used. If a certainamplification of the repetitive signal pattern is required it istherefore possible to use a certain length of the input signal in orderto achieve this certain amplification of the repetitive signal pattern.

To illustrate the above mentioned embodiment consider the followingexample:

A repetitive signal pattern with a lowest repetition frequency f₁ is ofinterest. In order to ensure detection of such a repetitive signal, itwill be necessary to produce an output signal capable of indicating acomplete cycle, i.e. it needs to represent a duration of T₁=1/f_(I).When consecutive output signal sample values are separated by a sampleperiod t_(delta) the minimum number of sample values in the outputsignal will be O_(Lengthmin)=T_(I)/t_(delta).

As mentioned above, the amount of amplification of the repetitive signalwill increase with the length of the input signal.

As mentioned above, the method described with reference to FIGS. 10 to13 above operates to enhance repetitive signal signatures in a sequenceof measurement data emanating from a rotating shaft. The wording“repetitive signal signature” is to be understood as being sample values[x(t), x(t+T), x, (t+2T), . . . x(t+nT)] including an amplitudecomponent having a non-stochastic amplitude value, and wherein aduration T between these sample values is constant, as long as the shaftrotates at a constant speed of rotation. With reference to FIG. 13 it isto be understood that digital values 4010 result from enhancing pluralrepetitive signal values in the input signal I (See FIG. 11), whereinthe input signal values are separated in time by a duration T_(IR).Hence, in that case it can be deduced that the “repetitive signalsignature” relates to a damage at the inner ring of the bearingassembly, when the period of repetition T_(IR) corresponds to a ballpass rate at the inner ring. Of course this presumes knowledge of theshaft diameter and the speed of rotation. Also, when there is such a“repetitive signal signature” signal component, there may be arepetitive signal component value x such that x(t) has similar amplitudeas x(t+T) which has similar amplitude as x(t+2T), which has similaramplitude as x(t+nT)x, and so on. When there is such a “repetitivesignal signature” present in the input signal, it may advantageously bedetected using the above described method, even when the repetitivesignal signature is so weak as to generate an amplitude componentsmaller than that of the stochastic signal components.

The method described in connection with FIGS. 10-13 may be performed bythe analysis apparatus 14 when the processor 50 executes thecorresponding program code 94, as discussed in conjunction with FIG. 4above. The data processor 50 may include a central processing unit forcontrolling the operation of the analysis apparatus 14, as well as aDigital Signal Processor (DSP). The DSP may be arranged to actually runthe program code 90 for causing the analysis apparatus 14 to execute theprogram 94 causing the process described above in connections with FIGS.10-13 to be executed. The Digital Signal Processor may be e.g. of thetype TMS320C6722, manufactured by Texas Instruments. In this manner theanalysis apparatus 14 may operate to execute all signal processingfunctions 94, including filtering function 240, enveloping function 250,decimation function 310 & 470 and enhancing function 320.

According to another embodiment of the invention, the signal processingmay be shared between the apparatus 14 and the computer 33, as mentionedabove. Hence, apparatus 14 may receive the analogue measurement signalS_(EA) and generate a corresponding digital signal S_(MD), and thendeliver the digital signal S_(MD) to control computer 33, allowingfurther signal processing functions 94 to be performed at the controllocation 31.

FIG. 10C illustrates an embodiment of enhancer 320. The enhancer 320 hasan input 315 on which it may receive a digital signal S_(RED) having asample rate f_(SRED) ⋅Enhancer 320 may include a signal handler 325adapted to receive the digital signal S_(RED) on a port 326. The signalhandler 325 also includes a port 327 for receiving a control valueindicative of the desired length I_(LENGTH) of the input signal I.

Enhancer 320 may also include a parameter setting means 330. Theparameter setting means 330 operates to generate relevant control valuesfor performing the desired signal enhancement. Hence the parametersetting means 330 has an output 332 for delivering the control valueI_(LENGTH) to signal handler 325.

Enhancer 320 may receive setting instructions on inputs 335. The settinginstructions received on inputs 335 may include data indicative of anorder value Y, data indicative of a frequency resolution Z, and dataindicative of an SNR improver value L. The inputs 335 may be coupled todeliver the received data to the parameter setting means 330 (See FIG.10C).

The enhancer 320 may be integrated in an analysis apparatus 14, asdescribed above e.g., with reference to FIG. 1.

Alternatively the enhancer 320 may be a part of the control computer 33at the central control location 31 (See FIG. 1). Accordingly digitalsignal S_(RED) having a sample rate f_(SRED) may be delivered to controlcomputer 33 on port 29B, e.g. from analysis apparatus 14 viacommunications network 18.

FIG. 10D illustrates signals according to an embodiment of the enhancermethod. A digital input signal I having a sample rate f_(SR) isschematically illustrated at the top of FIG. 10D. The digital inputsignal I includes at least I_(LENGTH) sample values, wherein I_(LENGTH)is a positive integer.

The execution of a calculation like that described by equation (5)above, may be illustrated as an operation involving a first signalportion S1 and a second signal portion S2.

The first signal portion S1 includes a copy of the first S_(1L) samplevalues in the input signal I. S_(1L)=I_(LENGTH)−O_(LENGTH)

The second signal portion S2 includes a copy of the last S_(2L) samplevalues in the input signal I. S_(2L)=I_(LENGTH)−S_(START)

The signal O_(S1) at the bottom of FIG. 10D is a schematic illustrationof an output signal O_(S1) obtained in response to a calculationinvolving the first signal portion S1 and the second signal portion S2.

FIG. 10E illustrates an embodiment of a method of operating the enhancer320.

In a step S310 the user interface 24B, 102, 104 prompts a user to enterenhancer setting values. According to an embodiment the user interfaceis adapted to request the user to indicate a desired frequencyresolution Z; and a desired highest repetition frequency f_(Dmax) to bedetected, and information indicative of a desired Signal Noise Ratioimprovement. The information indicative of desired SNR improvement maybe entered in the form of SNR improver value L. The desired highestrepetition frequency may be entered in the form of an order numberO_(VHigh), Y. In this context the order number O_(VHigh), Y is equal tothe relation (Y, O_(V), O_(VHIGH)) between a highest repetitionfrequency (f_(Dmax)) to be detectable and said speed of rotation(f_(ROT)):

O _(VHIGH) =Y=f _(Dmax) /f _(ROT)

According to an embodiment of the invention, the user interface 24B,102, 104 prompts the user to input a desired frequency resolution Z(step S310), and thereafter it is adapted to await input (step S320) inthe form of data indicative of a desired frequency resolution Z or inputin the form of data instructing the enhancer 320 to set the frequencyresolution Z automatically. If data indicative of a desired frequencyresolution Z is entered by the user, then the entered data will bedelivered to the parameter setter 330 (step S330). If the user entersdata indicating desire to let the frequency resolution Z beautomatically set, the user interface will indicate (Step S340) to theparameter setter 330 to set the frequency resolution Z to a defaultvalue.

Thereafter, the user interface 24B, 102, 104 prompts (S350) the user toinput a desired highest repetition frequency to be detected. The userinterface 24B, 102, 104 is then adapted to await input (step S360)indicative of a desired highest repetition frequency or input in theform of data instructing the enhancer 320 to set the highest repetitionfrequency automatically. If data indicative of a desired highestrepetition frequency is entered by the user, then the entered data willbe received and delivered to the parameter setter 330 (step S370). Ifthe user enters data indicating desire to let the highest repetitionfrequency be automatically set, the user interface will indicate (StepS380) to the parameter setter 330 to set the highest repetitionfrequency to a default value. The highest repetition frequency may beentered and/or set in the form of an order number O_(VHigh), Y. Asdiscussed above, the order value O_(VHigh), Y is a setting of thehighest repetition frequency to be detectable in the output signal Os tobe generated. When, for example the interesting bearing signals mayoccur about y times per revolution of the monitored shaft 8, 801A, 801B,801C, 803 the order value O_(VHigh), Y should be set to at least y.Using numbers, this means that when the interesting bearing signals mayoccur about 100 times per revolution of the monitored shaft 8, 801A,801B, 801C, 803 the order value O_(VHigh), Y should be set to at least100.

Thereafter, the user interface 24B, 102, 104 prompts (S390) the user toinput a desired SNR improvement. The user interface 24B, 102, 104 isthen adapted to await input (step S400) indicative of a desired SNRimprovement or input in the form of data instructing the enhancer 320 toset the SNR improvement automatically. If data indicative of SNRimprovement is entered by the user, then the entered data will bereceived and delivered to the parameter setter 330 (step S410). If theuser enters data indicating desire to let the SNR improvement beautomatically set, the user interface will indicate (Step S420) to theparameter setter 330 to set the SNR improvement to a default value. TheSNR improvement may be entered in the form of SNR improver value L.

The control values are delivered to the parameter setter 320 on ports335 (FIGS. 10C & 10E).

The parameter setter 330 includes a revolution calculator 340 coupled toreceive the control values Z and Y. The revolution calculator 340operates to calculate a value X_(E). The value X_(E) indicates how many“enhanced revolutions” of the monitored shaft 8, 801A, 801B, 801C, 803the samples in the output signal O_(S1) (See FIG. 10D and/or FIG. 12and/or FIG. 13) should correspond to. For example, when the frequencyresolution Z is set to 1600 and the order value is set to Y=100, thenaccording to an embodiment of the invention the samples in the outputsignal O_(S1) should correspond to X_(E)=Z/Y=16 “enhanced revolutions”of the monitored shaft 8, 801A, 801B, 801C, 803. Hence, the revolutioncalculator 340 has inputs for receiving data indicative of a frequencyresolution setting value Z and data indicative of a set order value Y.The revolution calculator 340 generates a data value X_(E) in responseto the frequency resolution setting value Z and the data indicative of aset order value Y.

The revolution calculator 340 delivers the data value X_(E) to an OutputSignal Length Calculator 345.

As illustrated in FIG. 10C, the enhancer has an input 350 for receivingdata indicative of the sample rate f_(SR) of the signal S_(RED) receivedon input 315. With reference to FIG. 9, FIG. 16 and FIG. 30, the samplerate value f_(SR) may correspond to the value f_(SR1) or f_(SR2).

The enhancer 320 may also have an input 360 for receiving dataindicative of a rotational speed f_(ROT). For some machines the speed ofrotation is preset to a constant value, and in such a case that speedvalue may be provided to input 360.

Alternatively a speed detector 420 (See FIG. 1 & FIG. 5 & FIG. 29) maybe provided to deliver a signal indicative of the speed of rotationf_(ROT) of the shaft 8. The speed of rotation f_(ROT) of the shaft 8 maybe provided in terms of revolutions per second, rps, i.e. Hertz (Hz). Asdiscussed below in connection with FIG. 19B and FIG. 30 the speed ofrotation values f_(ROT)(j) may be generated by a speed value generator601 in dependence on a position signal, according to embodiments of theinvention.

The Output Signal Length Calculator 345 operates to calculate a valueO_(L) indicative of the number of sample values O_(LENGTH) needed in theoutput signal O_(S1) (See FIG. 10D) in response to the received data,i.e. in response to the shaft “enhanced revolutions” value X_(E), theshaft rotational speed value f_(ROT) and the sample rate value f_(SR).

Hence, if X_(E)=16, the sample rate value f_(SR)=30.72 Hz and the shaftrotational speed value f_(ROT)=0,12 rps, then the number of samplevalues needed in the output signal O_(S1) will beO_(L)=X_(E)*f_(SR)/f_(ROT)=4096.

Hence, according to an embodiment, the minimum number of sample valuesO_(L) needed in the output signal O_(S1), S_(MDP) in order to enable asubsequent analysis of repetition frequencies up to order O_(VHigh), Ywith a frequency resolution Z can be calculated in dependence on theparameters Y, Z, f_(ROT) and f_(SR), wherein f_(SR) is a sample ratevalue such that the number of samples per revolution of the monitoredshaft 8, 801A, 801B, 801C, 803 is constant. The number of samples perrevolution of the monitored shaft is constant when the rotational speedis constant, and/or when a fractional decimator is used for compensatingfor a variable shaft speed, as discussed in further detailed later inthis document.

Accordingly the number of sample values O_(LENGTH) to be generated mustbe O_(L) or higher, wherein O_(L)=X_(E)*f_(SR)/f_(ROT).

The Output Signal Length Calculator 345 operates to calculate a valueO_(L) and to set the value O_(LENGTH). The value O_(LENGTH) is set to avalue equal to or greater than the calculated value O_(L).

The Output Signal Length Calculator 345 operates to deliver valueO_(LENGTH) to input 364 of an Input Signal Length Calculator 365. TheOutput Signal Length Calculator 345 also operates to deliver valueO_(LENGTH) to a stochastic signal frequency attenuator setting operator370. The stochastic signal frequency attenuator setting operator 370 isarranged to set a variable S_(START). The variable S_(START) controlsthe frequency limit for attenuation of stochastic signals.

As can be seen from FIG. 10D, the value S_(START) divided by the samplerate f_(SR) corresponds to a time period Ts:

T _(S) =S _(START) /f _(SR) =S _(START) *T _(SR)

Wherein T_(SR) may represent the duration of time between twoconsecutive samples.

S_(START) is the number of samples of delay or displacement betweensignals S1 and S2 to be correlated, as can also be seen in FIG. 10D.

When the variable S_(START) is set to the same value as O_(LENGTH) thenstochastic signals with a corresponding frequencyf_(STOCHASTIC_MAX)=1/Ts and higher frequencies will be attenuated in theoutput signal O, S_(MDP). Accordingly it is advantageous to set thevariable S_(START) to a value equal to O_(LENGTH) or to a value higherthan O_(LENGTH). Hence, stochastic signal frequency attenuator settingoperator 370 is arranged to set the variable S_(START) to a value equalto O_(LENGTH) or to a value higher than O_(LENGTH).

The Input Signal Length Calculator 365 operates to calculate a value ILand to set the value I_(LENGTH). The variable value IL is generated independence on the information indicative of desired SNR improvementwhich may be received on port 366, the value of the variable S_(START)which may be received on port 367 and the value O_(LENGTH) which may bereceived on port 364.

Hence, in order to be able to generate an output signal O, S_(MDP) fromthe enhancer 320 having O_(LENGTH) sample values, the enhancer mustreceive at least IL sample values on port 315. According to anembodiment the value of variable IL is:

I _(L) =O _(LENGTH) *L+S _(START) +O _(LENGTH)

Accordingly it is advantageous to set the variable I_(LENGTH) to a valueequal to IL or to a value higher than I_(L). Hence, Input Signal LengthCalculator 365 is arranged to set the variable I_(LENGTH) to a valueequal to I_(L) or to a value higher than I_(L). The Input Signal LengthCalculator 365 is arranged to deliver the control value TLENGTH onoutput 332 to the signal handler 325 (See FIG. 10C).

The Input Signal Length Calculator 365 is arranged to deliver thecontrol value I_(LENGTH) to an input of a Summing Determinator 375. Thesumming determinator 375 also has an input for receiving data indicativeof the variable S_(START). Moreover, the summing determinator 375 alsohas an input for receiving data indicative of the number of samplevalues O_(LENGTH) to be generated in the form of output signal OS1,S_(MDP). Accordingly, the Stochastic Signal Frequency Attenuator SettingOperator 370 is arranged to deliver data indicative of the variableS_(START) to the Summing Determinator 375, and Output Signal LengthCalculator 345 is arranged to deliver data indicative of the valueO_(LENGTH) to the Summing Determinator 375.

The Summing Determinator 375 is arranged to generate a value C_(LENGTH)in dependence on the values I_(LENGTH), O_(LENGTH) and S_(START).

The value C_(LENGTH) is set to a value substantially equal to thedifference between the value I_(LENGTH) and the sum of values S_(START)and O_(LENGTH) Hence, Summing Determinator 375 may deliver a valueC_(LENGTH)=I_(LENGTH)−S_(STAR)−O_(LENGTH).

The Summing Determinator 375 may be arranged to deliver the valueC_(LENGTH) on an output 377 of the parameter setting means 330.

FIG. 10G illustrates another embodiment of enhancer 320, wherein anembodiment 375B of the Summing Determinator has an input for receivingdata indicative of the number of sample values O_(LENGTH) to begenerated, and another input for receiving the SNR improver value L.Summing Determinator 375B is adapted to generate a value C_(LENGTH) independence on the values O_(LENGTH) and the SNR improver value L.Summing Determinator 375B is adapted to set C_(LENGTH)=L*O_(LENGTH)

The Summing Determinator 375B may be arranged to deliver the valueC_(LENGTH) on output 377 of the parameter setting means 330.

The Output Signal Length Calculator 345 also operates to deliver valueO_(LENGTH) on an output 379 of the parameter setting means 330.

As mentioned above, the signal handler 325 includes a port 326 forreceiving the digital time domain signal S_(RED), and a port 327 forreceiving a control value indicative of the desired length I_(LENGTH) ofthe input signal I.

Signal handler 325 cooperates with a memory 380 having plural memoryportions. According to an embodiment the memory may include a memoryportion 382 for storing at least I_(LENGTH) consecutive sample values ofthe signal S_(RED). Hence, Signal handler 325 may, in response toreceiving an activation signal on an activation input 384 operate toread the value I_(LENGTH) on input 327 and thereafter it operates toreceive

I_(LENGTH) consecutive sample values on port 326. The Signal handler 325may also, in response to receiving an activation signal on an activationinput 384, in cooperation with memory 380 operate to store these samplevalues in memory portion 382.

Hence, the content of memory portion 382 represents input signal I, asdepicted in FIG. 10D.

An output sample value generator 386 operates to generate a first signalportion S1 and a second signal portion S2 in dependence of input signalI.

In response to receiving the activation signal on activation input 388the output sample value generator 386 may operate to read samples I(i₀)to I(i₀+C_(LENGTH)), and to store these samples in a second memoryportion 390 as signal portion S1; and output sample value generator 386may operate to read samples I(i₀+S_(START)+1+1) toI(Sstart+Clength+Olength)) and to store these samples in a third memoryportion 392, wherein i₀ is a constant positive integer.

Hence, the content of memory portions 390 and 392, respectively, mayrepresent first signal portion S1 and a second signal portion S2, asdepicted in FIG. 10D. Thereafter output sample value generator 386 mayoperate to Cross correlate signals S1 and S2.

Alternatively, the correlation involves reading the sample values of theinput signal I as stored in memory portion 382, as schematicallyillustrated in FIG. 10C and at the top of FIG. 10D. With reference toFIG. 10F, the output sample value generator 386 may operate to performthe following steps:

Step S500: Set a variable t to a first value t₀. The first value t₀ maybe t₀=1.

Step S510: Calculate an output sample value:

${S_{MDP}(t)} = {\sum\limits_{i = {i\; 0}}^{i = {{i\; 0} + {CLENGTH} - 1}}{{I(i)}^{*}{I\left( {i + {Sstart} + t} \right)}}}$

Step S520: Deliver the generated output sample value S_(MDP)(t) onoutput port 394.

Step S530: Increase the counter value t, i.e. Set t:=t+1;

Step S540: Check if value t is greater than value O_(LENGTH)+t₀−1. Ifvalue t is greater than value O_(LENGTH)+t₀−1 then generate a signal toindicate that the complete output signal has been generated (Step S550).If value t is not greater than value O_(LENGTH)+t₀−1 then repeat stepS510, using the increased t-value.

FIG. 10H is a table for illustrating an embodiment of a part of thecalculation in step S510. The enhancer 320 is adapted to generate anoutput sample value S_(MDP)(t) in dependence on a plurality C_(LENGTH)of input signal products P(i,t). C_(LENGTH) is a positive integer.

With reference to table 1 (See FIG. 10H) an input signal product P(i,t)for an output sample position t is obtained by multiplying a first inputsample value I(i) at a first sample position i with a second inputsample value I(i+t+S_(START)). The second input sample value is found ata second sample position i+t+S_(START) in the input signal vector I (SeeFIG. 10D or FIG. 11). Hence, the second input sample value is separatedfrom said first input sample value by a certain number N_(C) of samplepositions. That certain number of sample positions may beN_(C)=(i+t+S_(START))−i=t+S_(START). Hence, the certain number N_(C) maybe equal to the sum of the output sample position value t and thecertain value S_(START).

As indicated above in connection with the description of FIG. 10D, thecertain value S_(START) is a number of sample positions which maycorrespond to a time period Ts. When the certain value S_(START) is setto the same value as O_(LENGTH) then stochastic signals with acorresponding frequency f_(STOCHASTIC_MAX) and higher frequencies willbe attenuated in the output signal S_(MDP). The value of this limitfrequency value f_(STOCHASTIC_MAX) is:

-   -   f_(STOCHASTIC_MAX)=1/Ts, wherein        -   Ts=S_(START)/f_(SR), wherein            -   f_(SR)=the sample rate of the input signal I.

Hence, according to a preferred embodiment, the certain number N_(C) isequal to, or larger than the certain value S_(START). Hence, accordingto a preferred embodiment, the difference N_(C) between the two indexvalues of the two terms in an input signal product P(i,t) is equal to,or larger than, the certain value S_(START).

In the above example, one term is first input sample value I(i) havingindex i, and the other term is second input sample valueI(i+t+S_(START)) having index value i+t+S_(START). In this connection itis of importance that the index values i, and i+t+S_(START),respectively, are values associated with sample values within the inputsignal vector I. Hence, the range I_(LENGTH) of input sample values andthe index values i, and i+t+S_(START), respectively, must be selected sothat the index values are values within the input signal vector. Withreference to the upper portion of FIG. 10D, which illustrates anembodiment of the input signal vector I, this means that the indexvalues i, and i+t+S_(START), respectively, must be values in the rangefrom i_(START) to i_(START)+I_(LENGTH)−1. Hence, if the constanti_(START) is set to i_(START)=1, then the index values i, andi+t+S_(START), respectively, must be values in the range from i=1 to1=I_(LENGTH).

The input signal I may include I_(LENGTH) sample values, as mentionedabove.

The enhancer receives an input signal vector having a first pluralityI_(LENGTH) of input sample values. This first plurality I_(LENGTH) ofinput sample values are processed so as to generate an output signalsequence S_(MDP) having a second plurality O_(LENGTH) of output samplevalues S_(MDP)(t); said second plurality being a positive integer.

An output sample value S_(MDP)(t) is calculated in dependence on a thirdplurality C_(LENGTH) input signal products P(i,t); said third plurality(C_(LENGTH)) being a positive integer.

As indicated above in equations (1) and (3), the following relation maybe used according to an embodiment:

I _(LENGTH) =O _(LENGTH) *L+S _(START) +O _(LENGTH)  (1)

and

C _(LENGTH) =I _(LENGTH) −S _(START) −O _(LENGTH)  (3)

As an example, the following numerical values may be used:

L=10

O_(LENGTH)=1024

S_(START)=1024

C_(LENGTH)=10240

I_(LENGTH)=12288

Hence, if for example, S_(START)=1024, and t varies from t=t_(MIN)=1 tot=t_(MAX)=O_(LENGTH)=1024, and the below equation (8) is used:

S _(MDP)(t)=Σ_(i=i0) ^(i=i0+CLENGTH-1) I(i)*I(i+Sstart+t)  (8)

then the difference N_(C) between the two index values of the two termswill vary from N_(C)=1025 to N_(C)=2048. This is since the highest indexvalue difference will beN_(CMAX)=S_(START)+t_(MAX)=S_(START)+O_(LENGTH)=1024+1024=2048; and thelowest index value difference will beNC_(MIN)=S_(START)+t_(MIN)=1024+1=1025.

Hence, if the constant i₀=1, the input signal vector I must then haveindex values ranging from i=i₀=1 to i=I_(LENGTH)=12288.

With reference to FIG. 10C, the output sample values S_(MDP)(t)delivered on output port 394 may be delivered to a memory 396, andmemory 396 may store the received sample values so that they arereadable as a sequence of output sample values OS1, S_(MDP), asschematically illustrated in the lower left corner in FIG. 10D.

Alternatively, the output sample values S_(MDP)(t) delivered on outputport 394 of output sample value generator 386 may be delivered directlyto output port 398 of enhancer 320.

According to another embodiment the equation for generating an outputsample value S_(MDP)(t) may be modified to read:

s _(MDP)(t)=Σ_(i=1+Sstart) ^(i=Ilength−Olength) I(i−Sstart)*I(i+t)  (9)

The above equation (9) will provide an output signal sequence O, S_(MDP)which is equivalent to the output signal sequence O, S_(MDP) generatedby equations (5) and (8) above. It can be shown that equation (9) is analternative manner of expressing equation (5).

Hence, also according to the equation (9) embodiment for generating anindividual output signal sample value S_(MDP)(t), the number of samplepositions Ne between the sample values to be multiplied will beN_(C)=t+S_(START).

Decimation of Sampling Rate

It may be desirable to provide a decimator 310 to reduce the samplingfrequency of the digital signal before delivery to the enhancer 320.Such a decimator 310 advantageously reduces the number of samples in thesignal to be analyzed, thereby reducing the amount of memory spaceneeded for storing the signal to be used. The decimation also enables afaster processing in the subsequent enhancer 320.

FIG. 14A illustrates a number of sample values in the signal deliveredto the input of the decimator 310, and FIG. 14B illustrates outputsample values of the corresponding time period. The signal being inputto decimator 310 may have a sampling frequency f_(S). As can be seen theoutput signal is has a reduced sample frequency f_(SR1). The decimator310 is adapted to perform a decimation of the digitally enveloped signalS_(ENV) so as to deliver a digital signal S_(RED) having a reducedsample rate f_(SR1) such that the output sample rate is reduced by aninteger factor 1 as compared to the input sample rate f_(S).

Hence, the output signal S_(RED) includes only every M:th sample valuepresent in the input signal S_(ENV). FIG. 14B illustrates an examplewhere M is 4, but M could be any positive integer. According to anembodiment of the invention the decimator may operate as described inU.S. Pat. No. 5,633,811, the content of which is hereby incorporated byreference.

FIG. 15A illustrates a decimator 310 according to an embodiment of theinvention. In the embodiment 310A of decimator 310 according to FIG.15A, a comb filter 400 filters and decimates the incoming signal at aratio of 16:1. That is, the output sampling rate is reduced by a firstinteger factor M1 of sixteen (M1=16) as compared to the input samplingrate. A finite impulse response (FIR) filter 401 receives the output ofthe comb filter 400 and provides another reduction of the sampling rateby a second integer factor M2. If integer factor M2=4, the FIR filter401 renders a 4:1 reduction of the sampling rate, and thereforedecimator 310A renders a total decimation of 64:1.

FIG. 15B illustrates another embodiment of the invention, whereinembodiment 310B of the decimator 310 includes a low pass filter 402,followed by a sample selector 403. The sample selector 403 is adapted topick every M:th sample out of the signal received from the low passfilter 402. The resulting signal S_(RED1) has a sample rate off_(SR1)=f_(S)/M, where f_(S) is the sample rate of received signalS_(ENV). The cutoff frequency of the low pass filter 402 is controlledby the value M.

According to one embodiment the value M is preset to a certain value.According to another embodiment the value M may be settable. Thedecimator 310 may be settable to make a selected decimation M:1, whereinM is a positive integer. The value M may be received on a port 404 ofdecimator 310.

The cut-off frequency of low pass filter 402 is f_(SR1)/(G*M) Hertz. Thefactor G may be selected to a value of two (2,0) or a value higher thantwo (2,0). According to an embodiment the value G is selected to a valuebetween 2,5 and 3. This advantageously enables avoiding aliasing. Thelow pass filter 402 may be embodied by a FIR filter.

The signal delivered by low pass filter 402 is delivered to sampleselector 403. The sample selector receives the value 1\1 on one port andthe signal from low pass filter 402 on another port, and it generates asequence of sample values in response to these inputs. The sampleselector is adapted to pick every M:th sample out of the signal receivedfrom the low pass filter 402. The resulting signal S_(RED1) has a samplerate of f_(SR1)=1/M*f_(S), where f_(S) is the sample rate of a signalS_(ENV) received on a port 405 of the decimator 310.

A Method for Compensating for Variable Shaft Speed

As mentioned above, a repetitive signal signature being present in theinput signal may advantageously be detected using the above describedmethod, even when the repetitive signal signature is so weak as togenerate an amplitude component smaller than that of the stochasticsignal components.

However, in certain applications the shaft rotational speed may vary.Performing autocorrelation using an input measurement sequence whereinthe speed of shaft rotation varies leads to deteriorated quality of theresulting output signal S_(MDP).

Accordingly an object of an aspect of the invention is to achieveequally high quality of the output signal S_(MDP) resulting fromautocorrelation when the rotational speed of the shaft varies, as whenthe rotational speed of the shaft is constant during the completemeasuring sequence, the data of which is autocorrelated.

FIG. 16 illustrates an embodiment of the invention including a decimator310 and an enhancer 320, as described above, and a fractional decimator470.

According to an embodiment of the invention, whereas the decimator 310operates to decimate the sampling rate by M:1, wherein M is an integer,the FIG. 16 embodiment includes a fractional decimator 470 fordecimating the sampling rate by U/N, wherein both U and N are positiveintegers. Hence, the fractional decimator 470 advantageously enables thedecimation of the sampling rate by a fractional number. According to anembodiment the values for U and N may be selected to be in the rangefrom 2 to 2000. According to an embodiment the values for U and N may beselected to be in the range from 500 to 1500. According to yet anotherembodiment the values for U and N may be selected to be in the rangefrom 900 to 1100.

In the FIG. 16 embodiment the output signal from the decimator 310 isdelivered to a selector 460. The selector enables a selection of thesignal to be input to the enhancer 320. When condition monitoring ismade on a rotating part having a constant speed of rotation, theselector 460 may be set in the position to deliver the signal S_(RED)having sample frequency f_(SR1) to the input 315 of enhancer 320, andfractional decimator 470 may be disabled. When condition monitoring ismade on a rotating part having a variable speed of rotation, thefractional decimator 470 may be enabled and the selector 460 is set inthe position to deliver the signal S_(RED2) having sample frequencyf_(SR2) to the input 315 of enhancer 320.

The fractional decimator 470 has an input 480. The input 480 may becoupled to receive the signal output from decimator 310. The fractionaldecimator 470 also has an input 490 for receiving information indicativeof the rotational speed of the shaft 8.

A speed detector 420 (See FIG. 5 & FIG. 1 & FIG. 29) may be provided todeliver a signal indicative of the speed of rotation f_(ROT) of theshaft 8. The speed signal may be received on a port 430 of theprocessing means 180, thereby enabling the processing means 180 todeliver that speed signal to input 490 of fractional decimator 470. Thespeed of rotation f_(ROT) of the shaft 8 may be provided in terms ofrotations per second, i.e. Hertz (Hz).

FIG. 17 illustrates an embodiment of the fractional decimator 470enabling the alteration of the sample rate by a fractional number U/N,wherein U and N are positive integers. This enables a very accuratecontrol of the sample rate f_(SR2) to be delivered to the enhancer 320,thereby enabling a very good detection of weak repetitive signalsignatures even when the shaft speed varies.

The speed signal, received on input 490 of fractional decimator 470, isdelivered to a Fractional Number generator 500. The Fractional Numbergenerator 500 generates integer number outputs U and Non outputs 510 and520, respectively. The U output is delivered to an upsampler 530. Theupsampler 530 receives the signal S_(RED) (See FIG. 16) via input 480.The upsampler 530 includes a sample introductor 540 for introducing U−1sample values between each sample value received on port 480. Each suchadded sample value is provided with an amplitude value. According to anembodiment each such added sample value is a zero (0) amplitude.

The resulting signal is delivered to a low pass filter 550 whose cut-offfrequency is controlled by the value U delivered by Fractional Numbergenerator 500. The cut-off frequency of low pass filter 550 isf_(SR2)/(K*U) Hertz. The factor K may be selected to a value of two (2)or a value higher than two (2).

The resulting signal is delivered to a Decimator 560. The Decimator 560includes a low pass filter 570 whose cutoff frequency is controlled bythe value N delivered by Fractional Number generator 500. The cut-offfrequency of low pass filter 570 is f_(SR2)/(K*N) Hertz. The factor Kmay be selected to a value of two (2) or a value higher than two (2).

The signal delivered by low pass filter 570 is delivered to sampleselector 580. The sample selector receives the value N on one port andthe signal from low pass filter 570 on another port, and it generates asequence of sample values in response to these inputs. The sampleselector is adapted to pick every N:th sample out of the signal receivedfrom the low pass filter 570. The resulting signal S_(RED2) has a samplerate of f_(SR)2=U/N*f_(SR1), where f_(SR1) is the sample rate of asignal S_(RED) received on pmt 480. The resulting signal S_(RED2) isdelivered on an output port 590.

The low pass filters 550 and 570 may be embodied by FIR filters. Thisadvantageously eliminates the need to perform multiplications with thezero-amplitude values introduced by sample introductor 540.

FIG. 18 illustrates another embodiment of the fractional decimator 470.The FIG. 18 embodiment advantageously reduces the amount of calculationneeded for producing the signal S_(RED2).

In the FIG. 18 embodiment the low pass filter 570 has been eliminated,so that the signal delivered by low pass filter 550 is delivereddirectly to sample selector 580. When the fractional decimator 470 isembodied by hardware the FIG. 18 embodiment advantageously reduces anamount of hardware, thereby reducing the cost of production.

When the fractional decimator 470 is embodied by software the FIG. 18embodiment advantageously reduces an amount of program code that need tobe executed, thereby reducing the load on the processor and increasingthe execution speed.

With reference to FIGS. 17 and 18, the resulting signal S_(RED2), whichis delivered on the output port of fractional decimator 470, has asample rate of f_(SR)2=U/N*f_(SR1), where f_(SR1) is the sample rate ofa signal S_(RED) received on port 480. The fractional value U/N isdependent on a rate control signal received on input port 490. Asmentioned above, the rate control signal may depend on a signalindicative of the speed of rotation of the shaft 8, which may bedelivered by speed detector 420 (See FIG. 1 and/or FIG. 5). The speeddetector 420 may be embodied by a device 420 providing a pulse signalwith a suitably selected resolution so as to enable the desired accuracyof the speed signal. In one embodiment the device 420 is adapted todeliver a full revolution marker signal once per full revolution of theshaft 8. Such a revolution marker signal may be in the form of anelectric pulse having an edge that can be accurately detected andindicative of a certain rotational position of the monitored shaft 8.According to another embodiment, the device 420 may deliver many pulsesignals per revolution of the monitored shaft.

According to an embodiment, the Fractional Number generator 500 controlsthe values of U and N so that the reduced sample rate FSR2 has such avalue as to provide a signal S_(RED2) wherein the number of samples perrevolution of the shaft 8 is substantially constant, irrespective of anyspeed variations of the shaft 8.

Accordingly: The higher the values of U and N, the better the ability ofthe fractional decimator 470 at keeping the number of sample values perrevolution of the shaft 8 at a is substantially constant value.

FIG. 19A illustrates decimator 310 and another embodiment of fractionaldecimator 470. Decimator 310 receives the signal S_(ENV) having asampling frequency f_(S) on a port 405, and an integer M on a port 404,as described above. Decimator 310 delivers a signal S_(RED1) having asampling frequency F_(SR1) on output 312, which is coupled to input 480of fractional decimator 470A. The output sampling frequency f_(SR1) is

f _(SR1) =f _(S) /M

wherein M is an integer.

Fractional decimator 470A receives the signal S_(RED1), having asampling frequency f_(SR1), as a sequence of data values S(j), and itdelivers an output signal S_(RED2) as another sequence of data valuesR(q) on its output 590.

Fractional decimator 470A may include a memory 604 adapted to receiveand store the data values S(j) as well as information indicative of thecorresponding speed of rotation f_(ROT) of the monitored rotating part.Hence the memory 604 may store each data value S(j) so that it isassociated with a value indicative of the speed of rotation of themonitored shaft at time of detection of the sensor signal S_(EA) valuecorresponding to the data value S(j).

Establishing an improved speed value

When Generating Output Data Values R(q) the Fractional Decimator 470A isadapted to read data values S(j) as well as information indicative ofthe corresponding speed of rotation f_(ROT) from the memory 604.

With reference to FIGS. 17 and 18, the resulting signal S_(RED2), whichis delivered on the output port of fractional decimator 470, has asample rate of

f _(SR2) =U/N*f _(SR1)

where f_(SR1) is the sample rate of a signal S_(RED) received on port480.

The fractional value U/N is dependent on a rate control signal receivedon input port 490. As mentioned above, the rate control signal may be asignal indicative of the speed of rotation of the shaft 8, which may bedelivered by speed detector 420 (See FIG. 1 and/or FIG. 5).

As mentioned above, the rate control signal may depend on a signalindicative of the speed of rotation of the shaft 8, which may bedelivered by speed detector 420 (See FIG. 1 and/or FIG. 5). The speeddetector 420 may be embodied by a device 420 providing a pulse signalwith a suitably selected resolution so as to enable the desired accuracyof the speed signal. In one embodiment the device 420 is adapted todeliver a full revolution marker signal once per full revolution of theshaft 8. Such a revolution marker signal may be in the form of anelectric pulse having an edge that can be accurately detected andindicative of a certain rotational position of the monitored shaft 8.According to another embodiment, the device 420 may deliver many pulsesignals per revolution of the monitored shaft 8.

The position signal, which may be referred to as an index pulse, can beproduced on an output of the device 420 in response to detection of azero angle pattern on an encoding disc that rotates when the monitoredshaft rotates. This can be achieved in several ways, as is well known tothe person skilled in the art. The encoding disc may e.g. be providedwith a zero angle pattern which will produce a zero angle signal witheach revolution of the disc. Correct interpretation of the positionsignal may also require gear ratio information. The gear ratioinformation may be indicative of about the rear ratio between themonitored part 8 and the rotating part of the device 420 that generatesthe position signal.

The speed variations may be detected e.g. by registering a “fullrevolution marker” in the memory 604 each time the monitored shaftpasses the certain rotational position, and by associating the “fullrevolution marker” with a sample value s(j) received at the sameinstant. In this manner the memory 604 will store a larger number ofsamples between two consecutive full revolution markers when the shaftrotates slower, since the A/D converter delivers a constant number,f_(S) or f_(RED1), of samples per second.

In effect, the condition analysis apparatus 14, 920 may be adapted torecord measurement data values S(j), encoder pulse signals Pi and timeinformation such that each measurement data value S(j) can be associatedwith data indicative of time and angular position. This, in turn, makesit possible to associate a very accurate speed value with eachmeasurement data value S(j).

According to an embodiment, the information about the positive edges ofencoder signal Pi s processed in parallel with the filtering 240,enveloping 250 and decimation 310 in a manner so as to maintain the timerelation between positive edges of the encoder signal P andcorresponding vibration sample values Se(i) and S(j). This signalprocessing is schematically illustrated by FIG. 30.

FIG. 19B is a block diagram of an embodiment of a speed value generator601. According to an embodiment the speed value generator 601 comprisesa memory 602. The speed value generator 601 is adapted to receive asequence of measurement values S(j) and a sequence of positionalsignals, together with temporal relations there-between, and the speedvalue generator 601 is adapted to provide, on its output, a sequence ofpairs SP of measurement values S(j) associated with corresponding speedvalues f_(ROT)(j). This is described in detail below.

FIG. 19C is a simplified illustration of an embodiment of the memory 602and its contents, and columns #01, #02, #03, #04 and #05, on the lefthand side of the memory 602 illustration, provide an explanatory imageintended to illustrate the temporal relation between the time ofdetection of the encoder pulse signals Pi (See column #02) and thecorresponding vibration measurement values S(j) (See column #05).

As mentioned above, the analogue-to-digital converter 40, 44 samples theanalogue electric measurement signal S_(EA) at an initial samplingfrequency f_(S) so as to generate a digital measurement data signalS_(MD). The encoder signal P may also be detected with substantially thesame initial temporal resolution f_(S), as illustrated in the column #02of FIG. 19C. This signal processing is also illustrated in FIG. 30, asdiscussed in detail in connection with the description of FIG. 30 below.Column #01 illustrates the progression of time as a series of timeslots, each time slot having a duration dt=1/f_(sample); whereinf_(sample) is a sample frequency having an integer relation to theinitial sample frequency f_(S) with which the analogue electricmeasurement signal S_(EA) is sampled. According to a preferredembodiment, the sample frequency f_(sample) is the initial samplefrequency f_(s). According to another embodiment the sample frequencyf_(sample) is the first reduced sampling frequency f_(SR1), which isreduced by an integer factor M as compared to the initial samplingfrequency f_(S).

In column #02 of FIG. 19B each positive edge of the encoder signal P isindicated by a figure “1”. In this example a positive edge of theencoder signal P is detected in the 3:rd, the 45:th, the 78:th time slotand in the 98:th time slot, as indicated in column #02. According toanother embodiment, the negative edges of the positional signal aredetected, which provides an equivalent result to detecting the positiveedges. According to yet another embodiment both the positive and thenegative edges of the positional signal are detected, so as to obtainredundancy by enabling the later selection of whether to use thepositive or the negative edge.

Column #03 illustrates a sequence of vibration sample values Se(i), asgenerated by the analogue-to-digital converter 40, 44, and column #05illustrates the corresponding sequence of vibration sample values S(j),as generated by the integer decimator 310. Hence, when the integerdecimator is set up to provide a total decimation factor M=10, therewill be provided one vibration sample value S(j) by decimator 310 forevery ten samples Se(i) fed into the integer decimator 310.

According to an embodiment, a very accurate position and timeinformation PT, relating to the decimated vibration sample value S(j),is maintained by setting the amplitude of the PositionTime signal incolumn #04 to value PT=3, so as to indicate that the positive edge (seecol#02) was detected in time slot #03. Hence, the amplitude value of thePositionTime signal, after the integer decimation stage 310 isindicative of the time of detection of the position signal edge P inrelation to sample value S(1).

In the example of FIG. 19B, the amplitude value of the PositionTimesignal at sample i=3 is PT=3, and since decimation factor M=10 so thatthe sample S(1) is delivered in time slot 10, this means that the edgewas detected M-PT=10−3=7 slots before the slot of sample S(1).

Accordingly, as illustrated in FIG. 30, the apparatus 14, 920 mayoperate to process the information about the positive edges of encodersignal P in parallel with the filtering 240, enveloping 250 anddecimation 310 of the vibration samples in a manner so as to maintainthe time relation between positive edges of the encoder signal P andcorresponding vibration sample values Se(i) and S(j) through the abovementioned signal processing from detection of the analogue signals tothe establishing of the speed values to be used by the fractionaldecimator.

FIG. 19D is a flow chart illustrating an embodiment of a method ofoperating the speed value generator 601 of FIG. 19B.

According to an embodiment, the speed value generator 601 analyses (StepS#10) the temporal relation between three successively received positionsignals, in order to establish whether the monitored rotational part 8is in a constant speed phase or in an acceleration phase. This analysismay be performed on the basis of information in memory 602, as describedabove (See FIG. 19C).

If the analysis reveals that there is an identical number of time slotsbetween the position signals, speed value generator concludes (in step#20) that the speed is constant, in which case step S#30 is performed.

In step S#30, the speed value generator may calculate the durationbetween two successive position signals, by multiplication of theduration of a time slot dt=1/f_(S) with the number of time slots betweenthe two successive position signals. When the position signal isprovided once per full revolution of the monitored part 8, the speed ofrevolution may be calculated as

V=1/(n _(diff) *dt),

wherein n_(diff)=the number of time slots between the two successiveposition signals. During constant speed phase, all of the sample valuesS(j) (see column #05 in FIG. 19C) associated with the three analyzedposition signals may be assigned the same speed value V=1/(n_(diff)*dt),as defined above. Thereafter, step S#10 may be performed again on thenext three successively received position signals.

Alternatively, when step S#10 is repeated, the previously third positionsignal P3 will be used a the first position signal P1 (i.e. P1:=P3), sothat it is ascertained whether any change of speed is at hand.

If the analysis (Step S#10) reveals that the number of time slotsbetween the 1:st and the 2:nd position signals differs from the numberof time slots between the 2:nd and 3:rd position signals, the speedvalue generator concludes, in step S#20) that the monitored rotationalpart 8 is in an acceleration phase.

In a next step S#40, the speed value generator 601 operates to establishmomentary speed values during acceleration phase, and to associate eachone of at the measurement data values S(j) with a momentary speed valueVp which is indicative of the speed of rotation of the monitored part atthe time of detection of the sensor signal (S_(EA)) value correspondingto that data value S(j).

FIG. 19E is a flow chart illustrating an embodiment of a method forperforming step S#40 of FIG. 19D. According to an embodiment, theacceleration is assumed to have a constant value for the durationbetween two mutually adjacent position indicators P (See column #02 inFIG. 19C). Hence, when

-   -   the position indicator P is delivered once per revolution, and    -   the gear ratio is 1/1: then    -   the angular distance travelled between two mutually adjacent        position indicators P is 1 revolution, which may also be        expressed as 360 degrees, and    -   the duration is T=n_(diff)*dt,        -   where n_(diff) is the number of slots of duration dt between            the two mutually adjacent position indicators P.

With reference to FIG. 19C, a first position indicator P was detected inslot i1=#03 and the next position indicator P was detected in sloti2=#45. Hence, the duration was n_(diff1)=i2−i1=45−3=42 time slots.

Hence, in step S#60 (See FIG. 19E in conjunction with FIG. 19C), thespeed value generator 601 operates to establish a first number of slotsn_(diff1) between the first two successive position signals P1 and P2,i.e. between position signal P(i=3) and position signal P(i=45).

In step S#70, the speed value generator 601 operates to calculate afirst speed of revolution value VT1. The first speed of revolution valueVT1 may be calculated as

VT1=1/(n _(diff1) *dt),

wherein VT1 is the speed expressed as revolutions per second,

n_(diff1)=the number of time slots between the two successive positionsignals; and

dt is the duration of a time slot, expressed in seconds.

Since the acceleration is assumed to have a constant value for theduration between two mutually adjacent position indicators P, thecalculated first speed value VT1 is assigned to the time slot in themiddle between the two successive position signals (step S#80).

Hence, in this example wherein first position indicator P1 was detectedin slot i_(P1)=#03 and the next position indicator P2 was detected inslot i_(P2)=#45; the first mid time slot is

slot i _(P1-2) =i _(P1)+(1_(P2) −i _(P1))/2=3+(45−3)/2=3+21)=24.

Hence, in step S#80 the first speed of revolution value VT1 may beassigned to a time slot (e.g. time slot i=24) representing a time pointwhich is earlier than the time point of detection of the second positionsignal edge P(i=45), see FIG. 19C.

The retro-active assigning of a speed value to a time slot representinga point in time between two successive position signals advantageouslyenables a significant reduction of the inaccuracy of the speed value.Whereas state of the art methods of attaining a momentary speed valuehave been satisfactory for establishing constant speed values at severalmutually different speeds of rotation, the state of the art solutionshave proven unsatisfactory when used for establishing speed values for arotating part during an acceleration phase.

By contrast, the methods according to embodiments of the inventionenable the establishment of speed values with an advantageously smalllevel of inaccuracy even during an acceleration phase.

In a subsequent step S#90, the speed value generator 601 operates toestablish a second number of slots n_(diff2) between the next twosuccessive position signals. In the example of FIG. 19C, that is thenumber of slots n_(diff2) between slot 45 and slot 78, i.e.n_(diff2)=78−45=33.

In step S#100, the speed value generator 601 operates to calculate asecond speed of revolution value VT2. The second speed of revolutionvalue VT2 may be calculated as

VT2=Vp61=1/(n _(diff2) *dt),

wherein n_(diff2)=the number of time slots between the next twosuccessive position signals P2 and P3. Hence, in the example of FIG.19C, n_(diff2)=33 i.e. the number of time slots between slot 45 and slot78.

Since the acceleration may be assumed to have a constant value for theduration between two mutually adjacent position indicators P, thecalculated second speed value VT2 is assigned (Step S#110) to the timeslot in the middle between the two successive position signals.

Hence, in the example of FIG. 19C, the calculated second speed value VT2is assigned to slot 61. Hence the speed at slot 61 is set to

V(61):=VT2.

Hence, in step S#110 the second speed value VT2 may be assigned to atime slot (e.g. time slot i=61) representing a time point which isearlier than the time point of detection of the third position signaledge P(i=78), see FIG. 19C.

Hence, in this example wherein one position indicator P was detected inslot i2=#45 and the next position indicator P was detected in sloti3=#78; the second mid time slot is the integer part of:

i _(P2-3) =i _(P2)+(i _(P3) −i _(P2))/2=45+(78−45)/2=45+33/2=61,5

Hence, slot 61 is the second mid time slot i_(P2-3).

In the next step S#120, a first acceleration value is calculated for therelevant time period. The first acceleration value may be calculated as:

a12=(VT2−VT1)/((i _(VT2) −i _(VT1))*dt)

In the example of FIG. 19C, the second speed value VT2 was assigned toslot 61, so i_(VT2)=61 and first speed value VT1 was assigned to slot24, so i_(VT1)=24.

Hence, since dt=1/f_(S), the acceleration value may be set to

a12=f _(S)*(VT2−VT1)/(i _(VT2) −i _(VT1))

for the time period between slot 24 and slot 60, in the example of FIG.19C.

In the next step S#130, the speed value generator 601 operates toassociate the established first acceleration value a12 with the timeslots for which the established acceleration value a12 is valid. Thismay be all the time slots between the slot of the first speed value VT1and the slot of the second speed value VT2. Hence, the established firstacceleration value a12 may be associated with each time slot of theduration between the slot of the first speed value VT1 and the slot ofthe second speed value VT2. In the example of FIG. 19C it is slots 25 to60. This is illustrated in column #07 of FIG. 19C.

In the next step S#140, the speed value generator 601 operates toestablish speed values for measurement values s(j) associated with theduration for which the established acceleration value is valid. Hencespeed values are established for each time slot which is

associated with a measurement value s(j), and

associated with the established first acceleration value a12.

During linear acceleration, i.e. when the acceleration a is constant,the speed at any given point in time is given by the equation:

V(i)=V(i−1)+a*dt,

wherein

V(i) is the momentary speed at the point of time of slot i

V(i−1) is the momentary speed at the point of time of the slotimmediately preceding slot i

a is the acceleration

dt is the duration of a time slot

According to an embodiment, the speed for each slot from slot 25 to slot60 may be calculated successively in this manner, as illustrated incolumn #08 in FIG. 19C. Hence, the momentary speed values to beassociated with the detected measurement values S(3), S(4), S(5), andS(6) associated with the acceleration value a12 may be established inthis manner.

According to another embodiment, the momentary speed for the slot 30relating to the first measurement value s(j)=S(3) may be calculated as:

V(i=30)=Vp30=VT1+a*(30−24)*dt=Vp24+a*6*dt

The momentary speed for the slot 40 relating to the first measurementvalue s(j)=S(4) may be calculated as:

V(i=40)=Vp40=VT1+a*(40−24)*dt=Vp40+a*16*dt

or as:

V(i=40)=Vp40=V(30)+(40−30)*dt=Vp30+a*10*dt

The momentary speed for the slot 50 relating to the first measurementvalue s(j)=S(5) may then subsequently be calculated as:

V(i=50)=Vp50=V(40)+(50−40)*dt=Vp40+a*10*dt

and the momentary speed for the slot 60 relating to the firstmeasurement value s(j)=S(6) may then subsequently be calculated as:

V(i=60)=Vp50+a*10*dt

When the measurement sample values S(j) associated with the establishedacceleration value have been associated with a momentary speed value, asdescribed above, an array of data including a time sequence ofmeasurement sample values S(j), each value being associated with a speedvalue V(j), f_(ROT)(j), is delivered on an output of said speed valuegenerator 601.

The time sequence of measurement sample values S(j), with associatedspeed values V(j), f_(ROT)(j) maybe used by the fractional decimator470, 470B of FIG. 17, 18 or 19A, e.g. when performing the methoddescribed with reference to FIGS. 21 and 22.

With reference to FIG. 19H, another embodiment of a method is described.According to this embodiment, the speed value generator operates torecord (see step S#160 in FIG. 19H) a time sequence of position signalvalues P_((i)) of said position signal (Ep) such that there is a firsttemporal relation n_(diff1) between at least some of the recordedposition signal values (P_((i))), such as e.g. between a first positionsignal value P1 _((i)) and a second position signal value P2 _((i)).According to an embodiment, the second position signal value P2 _((i))is received and recorded in a time slot (i) which arrives ndiff1 slotsafter the reception of the first position signal value P1 _((i)) (seestep S#160 in FIG. 19H). Then the third position signal value P1 _((i))is received and recorded (see step S#170 in FIG. 19H) in a time slot (i)which arrives ndiff2 slots after the reception of the second positionsignal value P2 _((i)).

As illustrated by step S#160 in FIG. 19H, the speed value generator mayoperate to calculate the relation value

a12=ndiff1/ndiff2

If the relation value equals unity, or substantially unity, then thespeed value generator operates to establish that the speed is constant,and it may proceed with calculation of speed according to a constantspeed phase method.

If the relation value a12 is higher than unity, the relation value isindicative of a percentual speed increase.

If the relation value a12 is lower than unity, the relation value isindicative of a percentual speed decrease.

FIG. 19F is a flow chart illustrating an embodiment of a method forperforming step S#40 of FIG. 19D. According to an embodiment, theacceleration is assumed to have a constant value for the durationbetween two mutually adjacent position indicators P (See column #02 inFIG. 19C). Hence, when

-   -   the position indicator P is delivered once per revolution, and    -   the gear ratio is 1/1: then        -   the angular distance travelled between two mutually adjacent            position indicators P is 1 revolution, which may also be            expressed as 360 degrees, and        -   the duration is T=n*dt,            -   where n is the number of slots of duration dt between                the first two mutually adjacent position indicators P1                and P2.

In a step S#200, the first speed of revolution value VT1 may becalculated as

VT1=1/(ndiff1*dt),

wherein VT1 is the speed expressed as revolutions per second,

ndiff1=the number of time slots between the two successive positionsignals; and

dt is the duration of a time slot, expressed in seconds. The value of dtmay e.g be the inverse of the initial sample frequency f_(S).

Since the acceleration is assumed to have a constant value for theduration between two mutually adjacent position indicators P, thecalculated first speed value VT1 is assigned to the first mid time slotin the middle between the two successive position signals P1 and P2.

In a step S#210, a second speed value VT2 may be calculated as

VT2=1/(ndiff2*dt),

wherein VT2 is the speed expressed as revolutions per second, ndiff2=thenumber of time slots between the two successive position signals; and

dt is the duration of a time slot, expressed in seconds. The value of dtmay e.g be the inverse of the initial sample frequency f_(S).

Since the acceleration is assumed to have a constant value for theduration between two mutually adjacent position indicators P, thecalculated second speed value VT2 is assigned to the second mid timeslot in the middle between the two successive position signals P2 andP3.

Thereafter, the speed difference V_(Delta) may calculated as

V _(Delta) =VT2−VT1

This differential speed V_(Delta) value may be divided by the number oftime slots between the second mid time slot and the first mid time slot.The resulting value is indicative of a speed difference dV betweenadjacent slots.

The momentary speed value to be associated with selected time slots maythen be calculated in dependence on said first speed of revolution valueVT1, and the value indicative of the speed difference between adjacentslots.

When the measurement sample values S(j), associated with time slotsbetween the first mid time slot and the second mid time slot, have beenassociated with a momentary speed value, as described above, an array ofdata including a time sequence of measurement sample values S(j), eachvalue being associated with a speed value V(j) is delivered on an outputof said speed value generator 601. The momentary speed value V(j) mayalso be referred to as f_(ROT)(j).

The time sequence of measurement sample values S(j), with associatedspeed values V(j), f_(ROT)(j) may be used by the fractional decimator470, 470B, e.g. when performing the method described with reference toFIGS. 21 and 22.

In summary, according to embodiments of the invention, a first momentaryspeed value VT1 may be established in dependence of

-   -   the angular distance delta-FI_(p1-p2) between a first positional        signal P1 and a second positional signal P2, and in dependence        of    -   the corresponding duration delta-T_(p1-p2)=t_(P2)−t_(P1).

Thereafter, a second momentary speed value VT2 may be established independence of

-   -   the angular distance delta-FI_(p1-p3) between the second        positional signal P2 and a third positional signal P3, and in        dependence of    -   the corresponding duration delta-T_(p2-p3)=t_(P2)−t_(p1).

Thereafter, momentary speed values for the rotational part 8 may beestablished by interpolation between the first momentary speed value VT1and the second momentary speed value VT2.

In other words, according to embodiments of the invention, two momentaryspeed values VT1 and VT2 may be established based on the angular.distances delta-FI_(p1-p2), delta-FI_(p2-p3) and the correspondingdurations between three consecutive position signals, and thereaftermomentary speed values for the rotational part 8 may be established byinterpolation between the first momentary speed value VT1 and the secondmomentary speed value VT2.

FIG. 19G is a graph illustrating a series of temporally consecutiveposition signals P1, P2, P3, . . . , each position signal P beingindicative of a full revolution of the monitored part 8. Hence, the timevalue, counted in seconds, increases along the horizontal axis towardsthe right.

The vertical axis is indicative of speed of rotation, graded inrevolutions per minute (RPTv1).

With reference to FIG. 19G, effects of the method according to anembodiment of the invention are illustrated. A first momentary speedvalue V(t₁)=VT1 may be established in dependence of

-   -   the angular distance delta-FI_(p1-p2) between the first        positional signal P1 and the second positional signal P2, and in        dependence of    -   the corresponding duration delta-T₁₋₂=t_(P2)−t_(P1). The speed        value attained by dividing the angular distance delta-FI_(p1-p2)        by the corresponding duration (t_(P2)−t_(P1)) represents the        speed V(t1) of the rotational part 8 at the first mid time point        t₁, also referred to as mtp (mid time point), as illustrated in        FIG. 19G.

Thereafter, a second momentary speed value V(t₂)=VT2 may be establishedin dependence of

-   -   the angular distance delta-FI between the second positional        signal P2 and a third positional signal P3, and in dependence of    -   the corresponding duration delta-T2-3=t_(P3)−t_(P2).

The speed value attained by dividing the angular distance delta-FI bythe corresponding duration (t_(P3)−t_(P2)) represents the speed V(t2) ofthe rotational part 8 at the 2:nd mid time point t₂(2:nd mtp), asillustrated in FIG. 19G.

Thereafter, momentary speed values for time values between the first midtime point and the 2:nd mid time point may be established byinterpolation between the first momentary speed value VT1 and the secondmomentary speed value VT2, as illustrated by the curve f_(ROTint).

Mathematically, this may be expressed by the following equation:

V(t12)=V(t1)+a*(t12−t1)

Hence, if the speed of the shaft 8 can be detected at two points of time(t1 and t2), and the acceleration a is constant, then the momentaryspeed at any point of time can be calculated. In particular, the speedV(t12) of the shaft at time t12, being a point in time after t₁ andbefore t₂, can be calculated by

V(t12)=V(t ₁)+a*(t12−t ₁)

wherein

a is the acceleration, and

t₁ is the first mid time point t₁ (See FIG. 19G).

The establishing of a speed value as described above, as well as thefractional decimation as described with reference to FIGS. 17, 18, 19A,21 and 22 may be attained by performing the corresponding method steps,and this may be achieved by means of a computer program 94 stored inmemory 60, as described above. The computer program may be executed by aDSP 50. Alternatively the computer program may be executed by a FieldProgrammable Gate Array circuit (FPGA).

The establishing of a speed value as described above, as well as thefractional decimation as described with reference to FIGS. 17, 18, 19A,21 and 22 may be performed by the analysis apparatus 14 when theprocessor 50 executes the corresponding program code 94, as discussed inconjunction with FIG. 4 above. The data processor 50 may include acentral processing unit 50 for controlling the operation of the analysisapparatus 14. Alternatively, the processor 50 may be embodied by aDigital Signal Processor (DSP) 50B. The DSP 50B may be arranged toactually run the program code 90 for causing the analysis apparatus 14to execute the program 94 causing the processes described above to beexecuted. According to another embodiment the processor 50B is a Fieldprogrammable Gate Array circuit (FPGA).

Fractional Decimation

The data values S(j) read from the memory 604 are delivered to sampleintroductor 540 for introducing U−1 sample values between each samplevalue received on port 480. Each such added sample value is providedwith an amplitude value. According to an embodiment each such addedsample value is a zero (0) amplitude.

The resulting signal is delivered to a low pass filter 550 whose cut-offfrequency is controlled by the value U delivered by Fractional Numbergenerator 500, as described above.

The resulting signal is delivered to the sample selector 580. The sampleselector receives the value Non one port and the signal from low passfilter 550 on another port, and it generates a sequence of sample valuesin response to these inputs. The sample selector is adapted to pickevery N:th sample out of the signal received from the low pass filter550. The resulting signal S_(RED2) has a sample rate off_(SR)2=U/N*f_(SR1), where f_(SR1) is the sample rate of a signalS_(RED) received on port 480. The resulting signal S_(RED2) is deliveredon output port 590.

Hence, the sampling frequency f_(SR2) for the output data values R(q) islower than input sampling frequency f_(SR1) by a factor D. D can be setto an arbitrary number larger than 1, and it may be a fractional number.According to preferred embodiments the factor D is settable to valuesbetween 1,0 to 20,0. In a preferred embodiment the factor D is afractional number settable to a value between about 1,3 and about 3,0.The factor D may be obtained by setting the integers U and N to suitablevalues. The factor D equals N divided by U:

D=N/U

According to an embodiment of the invention the integers U and N aresettable to large integers in order to enable the factor D=N/U to followspeed variations with a minimum of inaccuracy. Selection of variables Uand N to be integers larger than 1000 renders an advantageously highaccuracy in adapting the output sample frequency to tracking changes inthe rotational speed of the monitored shaft. So, for example, setting Nto 500 and U to 1001 renders D=2,002.

The variable D is set to a suitable value at the beginning of ameasurement and that value is associated with a certain speed ofrotation of a rotating part to be monitored. Thereafter, during thecondition monitoring session, the fractional value D is automaticallyadjusted in response to the speed of rotation of the rotating part to bemonitored so that the signal outputted on port 590 provides asubstantially constant number of sample values per revolution of themonitored rotating part.

As mentioned above, the encoder 420 may deliver a full revolution markersignal once per full revolution of the shaft 8. Such a full revolutionmarker signal may be in the form of an electric pulse having an edgethat can be accurately detected and indicative of a certain rotationalposition of the monitored shaft 8. The full revolution marker signal,which may be referred to as an index pulse, can be produced on an outputof the encoder 420 in response to detection of a zero angle pattern onan encoding disc that rotates when the monitored shaft rotates. This canbe achieved in several ways, as is well known to the person skilled inthis art. The encoding disc may e.g. be provided with a zero anglepattern which will produce a zero angle signal with each revolution ofthe disc. The speed variations may be detected e.g. by registering a“full revolution marker” in the memory 604 each time the monitored shaftpasses the certain rotational position, and by associating the “fullrevolution marker” with a sample value s(j) received at the sameinstant. In this manner the memory 604 will store a larger number ofsamples between two consecutive full revolution markers when the shaftrotates slower, since the A/D converter delivers a constant number ofsamples f_(S) per second.

FIG. 20 is a block diagram of decimator 310 and yet another embodimentof fractional decimator 470. This fractional decimator embodiment isdenoted 470B. Fractional decimator 470B may include a memory 604 adaptedto receive and store the data values S(j) as well as informationindicative of the corresponding speed of rotation f_(ROT) of themonitored rotating part. Hence the memory 604 may store each data valueS(j) so that it is associated with a value indicative of the speed ofrotation f_(ROT)(i) of the monitored shaft at time of detection of thesensor signal S_(EA) value corresponding to the data value S(j). Theprovision of data values S(j) associated with corresponding speed ofrotation values f_(ROT)(j) is described with reference to FIGS. 19A-19Gabove.

Fractional decimator 470B receives the signal S_(RED1), having asampling frequency f_(SR1), as a sequence of data values S(j), and itdelivers an output signal S_(RED2), having a sampling frequency f_(SR2),as another sequence of data values R(q) on its output 590.

Fractional decimator 470B may include a memory 604 adapted to receiveand store the data values S(J) as well as information indicative of thecorresponding speed of rotation f_(ROT) of the monitored rotating part.Memory 604 may store data values S(j) in blocks so that each block isassociated with a value indicative of a relevant speed of rotation ofthe monitored shaft, as described below in connection with FIG. 21.

Fractional decimator 470B may also include a fractional decimationvariable generator 606, which is adapted to generate a fractional valueD. The fractional value D may be a floating number. Hence, thefractional number can be controlled to a floating number value inresponse to a received speed value f_(ROT) so that the floating numbervalue is indicative of the speed value f_(ROT) with a certaininaccuracy. When implemented by a suitably programmed DSP, as mentionedabove, the inaccuracy of floating number value may depend on the abilityof the DSP to generate floating number values.

Moreover, fractional decimator 470B may also include a FIR filter 608.The FIR filter 608 is a low pass FIR filter having a certain low passcut off frequency adapted for decimation by a factor D_(MAX). The factorD_(MAX) may be set to a suitable value, e.g. 20,000. Moreover,fractional decimator 470B may also include a filter parameter generator610.

Operation of fractional decimator 470B is described with reference toFIGS. 21 and 22 below.

FIG. 21 is a flow chart illustrating an embodiment of a method ofoperating the decimator 310 and the fractional decimator 470B of FIG.20.

In a first step S2000, the speed of rotation F_(ROT) of the part to becondition monitored is recorded in memory 604 (FIGS. 20 & 21), and thismay be done at substantially the same time as measurement of vibrationsor shock pulses begin. According to another embodiment the speed ofrotation of the part to be condition monitored is surveyed for a periodof time. The highest detected speed F_(ROTmax) and the lowest detectedspeed F_(ROTmin) may be recorded, e.g. in memory 604 (FIGS. 20 & 21).

In step S2010, the recorded speed values are analysed, for the purposeof establishing whether the speed of rotation varies. If the speed isdetermined to be constant, the selector 460 (FIG. 16) may beautomatically set in the position to deliver the signal S_(RED) havingsample frequency f_(SR1) to the input 315 of enhancer 320, andfractional decimator 470, 470B may be disabled. If the speed isdetermined to be variable, the fractional decimator 470, 470B may beautomatically enabled and the selector 460 is automatically set in theposition to deliver the signal S_(RED2) having sample frequency f_(SR2)to the input 315 of enhancer 320.

In step S2020, the user interface 102,106 displays the recorded speedvalue f_(ROT) or speed values f_(ROTmin), f_(ROTmax), and requests auser to enter a desired order value O_(V). As mentioned above, the shaftrotation frequency f_(ROT) is often referred to as “order 1”. Theinteresting signals may occur about ten times per shaft revolution(Order 10). Moreover, it may be interesting to analyse overtones of somesignals, so it may be interesting to measure up to order 100, or order500, or even higher. Hence, a user may enter an order number O_(V) usinguser interface 102.

In step S2030, a suitable output sample rate f_(SR2) is determined.According to an embodiment output sample rate f_(SR2) is set tof_(SR)2=C*O_(V)*f_(ROTmin)

-   -   wherein    -   C is a constant having a value higher than 2,0    -   O_(V) is a number indicative of the relation between the speed        of rotation of the monitored part and the repetition frequency        of the signal to be analysed.    -   f_(ROTmin) is a lowest speed of rotation of the monitored part        to expected during a forthcoming measurement session. According        to an embodiment the value f_(ROTmin) is a lowest speed of        rotation detected in step S2020, as described above.

The constant C may be selected to a value of 2,00 (two) or higher inview of the sampling theorem. According to embodiments of the inventionthe Constant C may be preset to a value between 2,40 and 2,70.

-   -   wherein    -   k is a factor having a value higher than 2,0

Accordingly the factor k may be selected to a value higher than 2,0.According to an embodiment the factor C is advantageously selected suchthat 100*C/2 renders an integer. According to an embodiment the factor Cmay be set to 2,56. Selecting C to 2,56 renders 100*C=256=2 raised to 8.

In step S2040, the integer value M is selected dependent on the detectedspeed of rotation f_(ROT) of the part to be monitored. The value of Mmay be automatically selected dependent on the detected speed ofrotation of the part to be monitored such that the intermediate reducedsampling frequency f_(SR1) will be higher than the desired output signalsampling frequency f_(SR2). The value of the reduced sampling frequencyf_(SR1) is also selected depending on how much of a variation ofrotational speed there is expected to be during the measuring session.According to an embodiment the sample rate f_(S) of the A/D convertermay be 102.4 kHz. According to an embodiment, the integer value M may besettable to a value between 100 and 512 so as to render intermediatereduced sampling frequency f_(SR1) values between 1024 Hz and 100 Hz.

In step S2050, a fractional decimation variable value D is determined.When the speed of rotation of the part to be condition monitored varies,the fractional decimation variable value D will vary in dependence onmomentary detected speed value.

According to another embodiment of steps S2040 and S2050, the integervalue M is set such that intermediate reduced sampling frequency f_(SR1)is at least as many percent higher than f_(SR2) (as determined in stepS2030 above) as the relation between highest detected speed valuef_(ROTmax) divided by the lowest detected speed value f_(ROTmin).According to this embodiment, a maximum fractional decimation variablevalue DMAX is set to a value of D_(MAX)=f_(ROTmax)/f_(ROTmin), and aminimum fractional decimation variable value DMIN is set to 1,0.Thereafter a momentary real time measurement of the actual speed valuefROT is made and a momentary fractional value D is set accordingly.

-   -   f_(ROT) is value indicative of a measured speed of rotation of        the rotating part to be monitored

In step S2060, the actual measurement is started, and a desired totalduration of the measurement may be determined. This duration may bedetermined in dependence on the degree of attenuation of stochasticsignals needed in the enhancer. Hence, the desired total duration of themeasurement may be set so that it corresponds to, or so that it exceeds,the duration needed for obtaining the input signal I_(LENGTH), asdiscussed above in connection with FIGS. 10A to 13. As mentioned abovein connection with FIGS. 10A to 13, a longer input signal I_(LENGTH)renders the effect of better attenuation of stochastic signals inrelation to the repetitive signal patterns in the output signal.

The total duration of the measurement may also be determined independence on a desired number of revolutions of the monitored part.

When measurement is started, decimator 310 receives the digital signalS_(ENV) at a rate fs and it delivers a digital signal S_(RED1) at areduced rate f_(SR1)=f_(S)/M to input 480 of the fractional decimator.In the following the signal S_(RED1) is discussed in terms of a signalhaving sample values S(j), where j is an integer.

In step S2070, record data values S(i) in memory 604, and associate eachdata value with a speed of rotation value f_(ROT). According to anembodiment of the invention the speed of rotation value f_(ROT) is readand recorded at a rate f_(RR)=1000 times per second. The read & recordrate f_(RR) may be set to other values, dependent on how much the speedf_(ROT) of the monitored rotating part varies.

In a subsequent step S2080, analyze the recorded speed of rotationvalues, and divide the recorded data values S(j) into blocks of datadependent on the speed of rotation values. In this manner a number ofblocks of block of data values S(j) may be generated, each block of datavalues S(j) being associated with a speed of rotation value. The speedof rotation value indicates the speed of rotation of the monitored part,when this particular block data values S(j) was recorded. The individualblocks of data may be of mutually different size, i.e. individual blocksmay hold mutually different numbers of data values S(j).

If, for example, the monitored rotating part first rotated at a firstspeed f_(ROT1) during a first time period, and it thereafter changedspeed to rotate at a second speed f_(ROT2) during a second, shorter,time period, the recorded data values S(j) may be divided into twoblocks of data, the first block of data values being associated with thefirst speed value f_(ROT1), and the second block of data values beingassociated with the second speed value f_(ROT2). In this case the secondblock of data would contain fewer data values than the first block ofdata since the second time period was shorter.

According to an embodiment, when all the recorded data values S(j) havebeen divided into blocks, and all blocks have been associated with aspeed of rotation value, then the method proceeds to execute step S2090.

In step S2090, select a first block of data values S(j), and determine afractional decimation value D corresponding to the associated speed ofrotation value f_(ROT). Associate this fractional decimation value Dwith the first block of data values S(j).

According to an embodiment, when all blocks have been associated with acorresponding fractional decimation value D, then the method proceeds toexecute step S2090. Hence, the value of the fractional decimation valueD is adapted in dependence on the speed f_(ROT).

In step S2100, select a block of data values S(j) and the associatedfractional decimation value D, as described in step S2090 above.

In step S2110, generate a block of output values R in response to theselected block of input values S and the associated fractionaldecimation value D. This may be done as described with reference to FIG.22.

In step S2120, Check if there is any remaining input data values to beprocessed. If there is another block of input data values to beprocessed, then repeat step S2100. If there is no remaining block ofinput data values to be processed then the measurement session iscompleted.

FIGS. 22A, 22B and 22C illustrate a flow chart of an embodiment of amethod of operating the fractional decimator 470B of FIG. 20.

In a step S2200, receive a block of input data values S(j) and anassociated specific fractional decimation value D. According to anembodiment, the received data is as described in step S2100 for FIG. 21above. The input data values S(j) in the received block of input datavalues S are all associated with the specific fractional decimationvalue D.

In steps S2210 to S2390 the FIR-filter 608 is adapted for the specificfractional decimation value D as received in step S2200, and a set ofcorresponding output signal values R(q) are generated. This is describedmore specifically below.

In a step S2210, filter settings suitable for the specific fractionaldecimation value D are selected. As mentioned in connection with FIG. 20above, the FIR filter 608 is a low pass FIR filter having a certain lowpass cut off frequency adapted for decimation by a factor D_(MAX). Thefactor D_(MAX) may be set to a suitable value, e.g. 20.

A filter ratio value FR is set to a value dependent on factor D_(MAX)and the specific fractional decimation value Das received in step S2200.Step S2210 may be performed by filter parameter generator 610 (FIG. 20).

In a step S2220, select a starting position value x in the receivedinput data block s(j). It is to be noted that the starting positionvalue x does not need to be an integer. The FIR filter 608 has a lengthF_(LENGTH) and the starting position value x will then be selected independence of the filter length F_(LENGTH) and the filter ratio valueFR. The filter ratio value FR is as set in step S2210 above. Accordingto an embodiment, the starting position value x may be set to

x:=F _(LENGTH) /F _(R).

In a step S2230 a filter sum value SUM is prepared, and set to aninitial value, such as e.g. SUM:=0,0

In a step S2240 a position j in the received input data adjacent andpreceding position x is selected. The position j may be selected as theinteger portion of x.

In a step S2250 select a position Fpos in the FIR filter thatcorresponds to the selected position j in the received input data. Theposition Fpos may be a fractional number. The filter position Fpos, inrelation to the middle position of the filter, may be determined to be

Fpos=[(x−j)*F _(R)]

-   -   wherein F_(R) is the filter ratio value.

In step S2260, check if the determined filter position value Fpos isoutside of allowable limit values, i.e. points at a position outside ofthe filter. If that happens, then proceed with step S2300 below.Otherwise proceed with step S2270.

In a step S2270, a filter value is calculated by means of interpolation.It is noted that adjacent filter coefficient values in a FIR low passfilter generally have similar numerical values. Hence, an interpolationvalue will be advantageously accurate.

First an integer position value IFpos is calculated:

IFpos:=Integer portion of Fpos

The filter value Fval for the position Fpos will be:

Fval=A(IFpos)+[A(IFpos+1)−A(IFpos)]*[Fpos−Ifpos]

-   -   wherein A(IFpos) and A(IFpos+1) are values in a reference        filter, and the filter position Fpos is a position between these        values.

In a step S2280, calculate an update of the filter sum value SUM inresponse to signal position j:

SUM:=SUM+Fval*S(J)

In a step S2290 move to another signal position:

Setj:=j−1

Thereafter, go to step S2250.

In a step 2300, a position j in the received input data adjacent andsubsequent to position x is selected. This position j may be selected asthe integer portion of x. plus I (one), i.e j:=1+Integer portion of x

In a step S2310 select a position in the FIR filter that corresponds tothe selected position j in the received input data. The position Fposmay be a fractional number. The filter position Fpos, in relation to themiddle position of the filter, may be determined to be

Fpos=[(j−x)*F _(R)]

-   -   wherein F_(R) is the filter ratio value.

In step S2320, check if the determined filter position value Fpos isoutside of allowable limit values, i.e. points at a position outside ofthe filter. If that happens, then proceed with step S2360 below.Otherwise proceed with step S2330.

In a step S2330, a filter value is calculated by means of interpolation.It is noted that adjacent filter coefficient values in a FIR low passfilter generally have similar numerical values. Hence, an interpolationvalue will be advantageously accurate.

First an integer position value IFpos is calculated:

IFpos:=Integer portion of Fpos

The filter value for the position Fpos will be:

Fval(Fpos)=A(IFpos)+[A(IFpos+1)−A(IFpos)]*[Fpos−Ifpos]

-   -   wherein A(IFpos) and A(IFpos+1) are values in a reference        filter, and the filter position Fpos is a position between these        values.

In a step S2340, calculate an update of the filter sum value SUM inresponse to signal position j:

SUM:=SUM+Fval*S(J)

In a step S2350 move to another signal position:

Setj:=j+1

Thereafter, go to step S2310.

In a step S2360, deliver an output data value R(j). The output datavalue R(j) may be delivered to a memory so that consecutive output datavalues are stored in consecutive memory positions. The numerical valueof output data value R(j) is:

R(j):=SUM

In a step S2370, update position value x:

x:=x+D

In a step S2380, update position value j

j:=j+1

In a step S2390, check if desired number of output data values have beengenerated. If the desired number of output data values have not beengenerated, then go to step S2230. If the desired number of output datavalues have been generated, then go to step S2120 in the methoddescribed in relation to FIG. 21.

In effect, step S2390 is designed to ensure that a block of outputsignal values R(q), corresponding to the block of input data values Sreceived in step S2200, is generated, and that when output signal valuesR corresponding to the input data values S have been generated, thenstep S2120 in FIG. 21 should be executed.

The method described with reference to FIG. 22 may be implemented as acomputer program subroutine, and the steps S2100 and S2110 may beimplemented as a mam program.

Monitoring Condition of Gear Systems

It should be noted that embodiments of the invention may also be used tosurvey, monitor and detect the condition of gear systems. Someembodiments provide particularly advantageous effects when monitoringepicyclic gear systems comprising epicyclic transmissions, gears and/orgear boxes. This will be described more in detail below. Epicyclictransmissions, gears and/or gear boxes may also be referred to asplanetary transmissions, gears and/or gear boxes.

FIG. 23 is a front view illustrating an epicyclic gear system 700. Theepicyclic gear system 700 comprises at least one or more outer gears702, 703, 704 revolving around a central gear 701. The outer gears 702,703, 704 are commonly referred to as planet gears, and the central gear701 is commonly referred to as a sun gear. The epicyclic gear system 700may also incorporate the use of an outer ring gear 705, commonly alsoreferred to as an annulus. The planet gears 702, 703, 704 may comprise Pnumber of teeth 707, the sun gear 701 may comprise S number of teeth708, and the annulus 705 may comprise A number of teeth 706. The Anumber of teeth on the annulus 705 are arranged to mesh with the Pnumber of teeth on the planet gears 702, 703, 704, which in turn arealso arranged to mesh with the S number of teeth on the sun gear 701. Itshould however be noted that the sun gear 701 is normally larger thanthe planet gears 702, 703, 704, whereby the illustration shown in FIG.23 should not be construed as limiting in this respect. When there aredifferent sizes on the sun gear 701 and the planet gears 702, 703, 704,the analysis apparatus 14 may also distinguish between detectedconditions of different shafts and gears of the epicyclic gear system700, as will become apparent from the following.

In many epicyclic gear systems, one of these three basic components,that is, the sun gear 701, the planet gears 702, 703, 704 or the annulus705, is held stationary. One of the two remaining components may thenserve as an input and provide power to the epicyclic gear system 700.The last remaining component may then serve as an output and receivepower from the epicyclic gear system 700. The ratio of input rotation tooutput rotation is dependent upon the number of teeth in each gear, andupon which component is held stationary.

FIG. 24 is a schematic side view of the epicyclic gear system 700 ofFIG. 23, as seen in the direction of the arrow SW in FIG. 23. Anexemplary arrangement 800, including the epicyclic gear system 700, maycomprise at least one sensor 10 and at least one analysis apparatus 14according to the invention as described above. The arrangement 800 may,for example, be used as gear box for wind turbines.

In an embodiment of the arrangement 800, the annulus 705 is held fixed.A rotatable shaft 801 has plural movable arms or carriers 801A, 801B,801C arranged to engage the planet gears 702, 703, 704. Upon providingan input rotation 802 to the rotatable shaft 801, the rotatable shaft801 and the movable arms 801A, 801B, 801C and the planet gears 702, 703,704 may serve as an input and provide power to the epicyclic gear system700. The rotatable shaft 801 and the planet gears 702, 703, 704 may thenrotate relative to the sun gear 701. The sun gear 701, which may bemounted on a rotary shaft 803, may thus serve as an output and receivepower from the epicyclic gear system 700. This configuration willproduce an increase in gear ratio

$G = {1 + {\frac{A}{S}.}}$

As an example, the gear ratio G when used as a gear box in a windturbine may be arranged such that the output rotation is about 5-6 timesthe input rotation. The planet gears 702, 703, 704 may be mounted, viabearings 7A, 7B and 7C, respectively, on the movable arms or carriers801A, 801B and 801C (as shown in both FIGS. 23-24). The rotatable shaft801 may be mounted in bearings 7D. Similarly, the rotary shaft 803 maybe mounted in bearings 7E, and the sun gear 701 may be mounted, viabearings 7F, on the rotary shaft 803.

According to one embodiment of the invention, the at least one sensor 10may be attached on or at a measuring point 12 of the fixed annulus 705of the epicyclic gear system 700. The sensor 10 may also be arranged tocommunicate with the analysis apparatus 14. The analysis apparatus 14may be arranged to analyse the condition of the epicyclic gear system700 on the basis of measurement data or signal values delivered by thesensor 10 as described above in this document. The analysis apparatus 14may include an evaluator 230 as above.

FIG. 25 illustrates an analogue version of an exemplary signal producedby and outputted by the pre-processor 200 (see FIG. 5 or FIG. 16) inresponse to signals detected by the at least one sensor 10 upon rotationof the epicyclic gear system 700 in the arrangement 800. The signal isshown for a duration of T_(REV), which represents signal values detectedduring one revolution of the rotatable shaft 801. It is to be understoodthat the signal delivered by the pre-processor 200 on port 260 (see FIG.5 and FIG. 16) may be delivered to input 220 of the evaluator 230 (seeFIG. 8 or FIG. 7).

As can be seen from the signal in FIG. 25, the amplitude or signaloutput of the signal increases as each of the planet gears 702, 703, 704passes the measuring point 12 of the sensor 10 in the arrangement 800.These portions of the signal are referred to in the following as thehigh amplitude regions 702A, 703A, 704A, which may comprise highamplitude spikes 901. It can also be shown that the total amount ofspikes 901, 902 in the signal over one revolution of the rotatable shaft801, i.e. during the time period T_(REV), directly correlates to theamount of teeth on the annulus 705. For example, if number of teeth onthe annulus 705 is A=73, the total number of spikes in the signal duringa time period T_(REV) will be 73; or if number of teeth on the annulus705 is A=75, the total number of spikes in the signal during a timeperiod T_(REV) will be 75, etc. This has been shown to be true providedthat there are no errors or faults in the gears 702, 703, 704, 705 ofthe arrangement 800.

FIG. 26 illustrates an example of a portion of the high amplitude region702A of the signal shown in FIG. 25. This signal portion may begenerated when the planet gear 702 passes its mechanically nearestposition to the measuring point 12 and the sensor 10 (see FIGS. 23-24).It has been noted that small periodic disturbances or vibrations 903,which are illustrated in FIG. 26, may sometimes occur. Here, the smallperiodic disturbances 903 have been linked to the occurrence of errors,faults or tears in the bearings 7A, as shown in FIGS. 23-24, which maybe mounted to one of the movable arms 801A. The small periodicdisturbances 903 may thus propagate (or translate) from a bearing 7Athrough the planet gear 702 of the epicyclic gear system 700, to theannulus 705 where the small periodic disturbances 903 may be picked upby the sensor 10 as described above e.g. in connection with FIGS. 1-24.Similarly, errors, faults or tears in the bearings 7B or 7C mounted toone of the movable arms 801B or 801C may also generate such smallperiodic disturbances 903 which in the same manner as above may bepicked up by the sensor 10. It should also be noted that the smallperiodic disturbances 903 may also emanate from errors, faults or tearsin the bearings 7F which may be mounted to the rotary shaft 803. Thedetection of these small periodic disturbances in the signal may beindicative of the bearings 7A, 7B, 7C and/or 7F beginning todeteriorate, or indicative of their being on the limit of their activelifespan. This may, for example, be important since it may help predictwhen the epicyclic gear system 700 and/or the arrangement 800 are inneed of maintenance or replacement.

According to an embodiment of the invention, the condition analyser 290in the evaluator 230 of the analysis apparatus 14 may be arranged todetect these small periodic disturbances 903 in the received signal fromthe sensor 10. This is made possible by the previously describedembodiments of the invention. The small periodic disturbances 903 mayalso be referred to as shock pulses 903 or vibrations 903. According toan embodiment of the invention, the analysis apparatus 14 employing anenhancer 320 as described above enables the detection of these shockpulses 903 or vibrations 903 originating from bearings 7A (or 7B, 7C or7F) using a sensor 10 mounted on the annulus 705 as described above.Although the mechanical shock pulse or vibration signal as picked up bythe sensor 10 attached to annulus 705 may be weak, the provision of anenhancer 320 as described above makes it possible to monitor thecondition of bearings 7A (or 7B, 7C or 7F) even though the mechanicalshock pulse or vibration signal has propagated via one or several of theplanet gears 702, 703 or 704.

As previously mentioned and shown in FIGS. 7-9, the condition analyser290 may be arranged to perform suitable analysis by operating on asignal in the time domain, or a signal in the frequency domain. However,the detection of the small periodic disturbances 903 in the receivedsignal from the sensor 10 is most fittingly described in frequencydomain, as shown in FIG. 27.

FIG. 27 illustrates an exemplary frequency spectrum of a signalcomprising a small periodic disturbance 903 as illustrated in FIG. 26.The frequency spectrum of the signal comprises a peak 904 at a frequencywhich is directly correlated with the engagement or meshing of the teethof the planet gears 702, 703, 704 and the annulus 705. In fact, thefrequency of the peak 904 in the frequency spectrum will be located atA×Ω, where

-   -   A is the total number of teeth of the annulus 705, and    -   Ω is the number of revolutions per second by the rotatable shaft        801, when rotation 802 occurs at a constant speed of rotation.

In addition to the peak 904 in the frequency spectrum, the smallperiodic disturbance 903 as illustrated in FIG. 26 may generate peaks905, 906 at the frequencies f₁, f2 centered about the peak 904 in thefrequency spectrum. The peaks 905, 906 at the frequencies f₁, f2 maythus also be referred to as a symmetrical sideband about the centre peak904. According to an exemplary embodiment of the invention, thecondition analyser 290 may be arranged to detect the one or severalpeaks in the frequency spectrum, and thus be arranged to detect smallperiodic disturbances in the signal received from the sensor 10. It canalso be shown that the peaks 905, 906 at the frequencies f₁, f2 relateto the centre peak 904 according to the equations Eq.1-2:

f ₁=(A×Ω)−(f _(D) ×f ₇₀₂)  (Eq. 1)

f ₂=(A×Ω)−(f _(D) ×f ₇₀₂)  (Eq. 2)

-   -   wherein    -   A is the total number of teeth of the annulus 705;    -   Ω is the number of revolutions per second by the rotatable shaft        801; and    -   f_(D) is a repetition frequency of the repetitive signal        signature which may be indicative of a deteriorated condition;        and    -   f₇₀₂ is the number of revolutions per second by the planet 702        around its own centre.

The repetition frequency f_(D) of the repetitive signal signature isindicative of the one of the rotating parts which is the origin of therepetitive signal signature. The repetition frequency f_(D) of therepetitive signal signature can also be used to distinguish betweendifferent types of deteriorated conditions, as discussed above e.g. inconnection with FIG. 8. Accordingly, a detected repetition frequencyf_(D) of the repetitive signal signature may be indicative of aFundamental train frequency (FTF), a Ball spin (BS) frequency, an OuterRace (OR) frequency, or an Inner Race (IR) frequency relating to abearing 7A, 7B, 7C or 7F in the epicyclic gear system 700 in thearrangement 800 in FIG. 24.

Hence, as described above, a data signal representing mechanicalvibrations emanating from rotation of one or several shafts, such as,rotatable shaft 801 and/or rotary shaft 803 (see FIGS. 23-24), mayinclude several repetitive signal signatures, and a certain signalsignature may thus be repeated a certain number of times per revolutionof one of the monitored shafts. Moreover, several mutually differentrepetitive signal signatures may occur, wherein the mutually differentrepetitive signal signatures may have mutually different repetitionfrequencies. The method for enhancing repetitive signal signatures insignals, as described above, advantageously enables simultaneousdetection of many repetitive signal signatures having mutually differentrepetition frequencies. This advantageously enables the simultaneousmonitoring of several bearings 7A, 7B, 7C, 7F associated with differentshafts 801, 803 using a single detector 10. The simultaneous monitoringmay also use the fact that the size of the sun gear 701 and the planetgears 702, 703, 704 normally are of different sizes, which further mayenable an easy detection of which of the bearings 7A, 7B, 7C, 7F inFIGS. 23-24 it is that is generating the small periodic disturbance 903,and thus which of the bearings 7A, 7B, 7C, 7F in FIGS. 23-24 may be inneed of maintenance or replacement. The method for enhancing repetitivesignal signatures in signals, as described above, also advantageouslymakes it possible to distinguish between e.g. a Bearing Inner Racedamage signature and a Bearing Outer Race damage signature in a singlemeasuring and analysis session.

The relevant value for Ω representing the speed of rotation of theplanet gears 702, 703, 704, can be indicated by a sensor 420 (see FIG.24). The sensor 420 may be adapted to generate a signal indicative ofrotation of the shaft 803 in relation to the annulus 705, and from thissignal the relevant value for Ω can be calculated when the number ofteeth of the annulus 705, the planet gears 702, 703, 704 and the sungear 701 are known.

FIG. 28 illustrates an example of a portion of the exemplary signalshown in FIG. 25. This exemplary portion demonstrates another example ofan error or fault which the condition analyser 290 also may be arrangedto detect in a similar manner as described above. If a tooth in the oneor several of the gears 701, 702, 703, 704, 705 should break or besubstantially worn down, the condition analyser 290 may be arrangeddetect that a tooth is broken or worn down since this will also generatea periodic disturbance, i.e. due to the lack of tooth engagement ormeshing of the missing or worn down tooth. This may be detectable by thecondition analyser 290 in, for example, the frequency spectrum of thesignal received from the sensor 10. It should also be noted that thistype of error or fault may be detected by the condition analyser 290 inany type of gear and/or gear system. The frequency of this type of teethengagement error, or meshing error, in a gear and/or gear system isoften located at significantly higher frequency than, for example, thefrequencies f₁, f2 in FIG. 27.

FIG. 29 illustrates yet an embodiment of a condition analyzing system 2according to an embodiment of the invention. The sensor 10 is physicallyassociated with a machine 6 which may include a gear system 700 havingplural rotational parts (See FIG. 1 & FIG. 29). The gear system of FIG.29 may be the epicyclic gear system 700 of FIG. 24. The epicyclic gearsystem 700 may, for example, be used as gear box for wind turbines.

The sensor unit 10 may be a Shock Pulse Measurement Sensor adapted toproduce an analogue signal S_(EA) including a vibration signal componentdependent on a vibrational movement of a rotationally movable part inthe gear system 700. The sensor 10 is delivers the analogue signalS_(EA) to a signal processing arrangement 920.

Signal processing arrangement 920 may include a sensor interface 40 anda data processing means 50. The sensor interface 40 includes an A/Dconverter 44 (FIG. 2A, FIG. 2B) generating the digital measurementsignal S_(MD). The A/D converter 44 is coupled to the data processingmeans 50 so as to deliver the digital measurement data signal S_(MD) tothe data processing means 50.

The data processing means 50 is coupled to a user interface 102. Theuser interface 102 may include user input means 104 enabling a user toprovide user input. Such user input may include selection of a desiredanalysis function 105, 290, 290T, 290F (FIG. 4, FIG. 7, FIG. 8), and/orsettings for signal processing functions 94, 250, 310, 470, 470A, 470B,320, 294 (See FIG. 4, FIG. 30).

The user interface 102 may also include a display unit 106, as describede.g. in connection with FIG. 2A an FIG. 5.

FIG. 30 is a block diagram illustrating the parts of the signalprocessing arrangement 920 of FIG. 29 together with the user interface102, 104 and the display 106.

The sensor interface 40 comprises an input 42 for receiving an analoguesignal S_(EA) from a sensor 10, and an A/D converter 44. A signalconditioner 43 (FIG. 2B) may optionally also be provided. The sensor maybe a Shock Pulse Measurement Sensor. The A/D converter 44 samples thereceived analogue signal with a certain sampling frequency f_(S) so asto deliver a digital measurement data signal S_(MD) having said certainsampling frequency f_(S).

The sampling frequency f_(S) may be set to

f _(S) =k*f _(SEAmax)

-   -   wherein    -   k is a factor having a value higher than 2,0

Accordingly the factor k may be selected to a value higher than 2,0.Preferably factor k may be selected to a value between 2,0 and 2,9 inorder to avoid aliasing effects. Selecting factor k to a value higherthan 2,2 provides a safety margin in respect of aliasing effects, asmentioned above in this document. Factor k may be selected to a valuebetween 2,2 and 2,9 so as to provide said safety margin while avoidingto generate unnecessarily many sample values. According to an embodimentthe factor k is advantageously selected such that 100*k/2 renders aninteger. According to an embodiment the factor k may be set to 2,56.Selecting k to 2,56 renders 100*k=256=2 raised to 8.

According to an embodiment the sampling frequency f_(S) of the digitalmeasurement data signal S_(MD) may be fixed to a certain value f_(S),such as e.g. f_(S)=102.4 kHz

Hence, when the sampling frequency f_(S) is fixed to a certain valuef_(S), the frequency f_(SEAmax) of the analogue signal S_(EA) will be:

f _(SEAmax) =f _(S) /k

-   -   wherein f_(SEAmax) is the highest frequency to be analyzed in        the sampled signal.

Hence, when the sampling frequency f_(S) is fixed to a certain valuef_(S)=102.4 kHz, and the factor k is set to 2,56, the maximum frequencyf_(SEAmax) of the analogue signal S_(EA) will be:

f _(SEAmax) =f _(S) /k=102 400/2,56=40 kHz

The digital measurement data signal S_(MD) having sampling frequencyf_(S) is received by a filter 240. According to an embodiment, thefilter 240 is a high pass filter having a cut-off frequency f_(LC). Thisembodiment simplifies the design by replacing the band-pass filter,described in connection with FIG. 6, with a high-pass filter 240. Thecut-off frequency f_(LC) of the high pass filter 240 is selected toapproximately the value of the lowest expected mechanical resonancefrequency value f_(RMU) of the resonant Shock Pulse Measurement sensor10. When the mechanical resonance frequency f_(RMU) is somewhere in therange from 30 kHz to 35 kHz, the high pass filter 240 may be designed tohaving a lower cutoff frequency f_(LC)=30 kHz. The high-pass filteredsignal is then passed to the rectifier 270 and on to the low pass filter280.

According to an embodiment it should be possible to use sensors 10having a resonance frequency somewhere in the range from 20 kHz to 35kHz. In order to achieve this, the high pass filter 240 may be designedto having a lower cutoff frequency f_(LC)=20 kHz.

The output signal from the digital filter 240 is delivered to a digitalenveloper 250.

Whereas prior art analogue devices for generating an envelope signal inresponse to a measurement signal employs an analogue rectifier whichinherently leads to a biasing error being introduced in the resultingsignal, the digital enveloper 250 will advantageously produce a truerectification without any biasing errors. Accordingly, the digitalenvelop signal S_(ENV) will have a good Signal-to-Noise Ratio, since thesensor being mechanically resonant at the resonance frequency in thepassband of the digital filter 240 leads to a high signal amplitude.Moreover, the signal processing being performed in the digital domaineliminates addition of noise and eliminates addition of biasing errors.

According an embodiment of the invention the optional low pass filter2801 n enveloper 250 may be eliminated. In effect, the optional low passfilter 2801 n enveloper 250 is eliminated since decimator 310 includes alow pass filter function. Hence, the enveloper 250 of FIG. 30effectively comprises a digital rectifier 270, and the signal producedby the digital rectifier 270 is delivered to integer decimator 310,which includes low pass filtering.

The Integer decimator 310 is adapted to perform a decimation of thedigitally enveloped signal S_(ENV) so as to deliver a digital signalS_(RED) having a reduced sample rate f_(SR1) such that the output samplerate is reduced by an integer factor M as compared to the input samplerate f_(S).

The value M may be settable in dependence on a detected speed ofrotation f_(ROT). The decimator 310 may be settable to make a selecteddecimation M:1, wherein M is a positive integer. The value M may bereceived on a port 404 of decimator 310. The integer decimation isadvantageously performed in plural steps using Low pass Finite ImpulseResponse Filters, wherein each FIR Filter is settable to a desireddegree of decimation. An advantage associated with performing thedecimation in plural filters is that only the last filter will need tohave a steep slope. A steep slope FIR filter inherently must have manytaps, i.e. a steep FIR filter must be a long filter. The number of FIRtaps, is an indication of

1) the amount of memory required to implement the filter,

2) the number of calculations required, and

3) the amount of “filtering” the filter can do; in effect, more tapsmeans more stopband attenuation, less ripple, narrower filters, etc.Hence the shorter the filter the faster it can be executed by the DSP50. The length of a FIR filter is also proportional to the degree ofachievable decimation. Therefore, according to an embodiment of theinteger decimator, the decimation is performed in more than two steps.

According to a preferred embodiment the integer decimation is performedin four steps: M1, M2, M3 & M4. The total decimation M equalsM1*M2*M3*M4 This may achieved by providing a bank of different FIRfilters, which may be combined in several combinations to achieve adesired total decimation M. According to an embodiment there are eightdifferent FIR filters in the bank.

Advantageously, the maximum degree of decimation in the last, 4:th, stepis five (M4=5), rendering a reasonably short filter having just 201taps. In this manner the FIR filters in steps 1, 2 and 3 can be allowedto have an even lower number of taps. In fact this allows for thefilters in steps 1, 2 and 3 to have 71 taps each or less. In order toachieve a total decimation of M=4000, it is possible to select the threeFIR-filters providing decimation M1=10, M2=10 and M3=10, and the FIRfilter providing decimation M4=4. This renders an output sample ratef_(SR1)=25,6, when f_(S)=102400 Hz. and a frequency range of 10 Hz.These four FIR filters will have a total of 414 taps, and yet theresulting stopband attenuation is very good. In fact, if the decimationof M=4000 were to be made in just one single step it would have requiredabout 160 000 taps to achieve an equally good stop band attenuation.

Output 312 of integer Decimator 310 is coupled to the speed valuegenerator 610 (See FIG. 30 in conjunction with FIG. 19B).

As illustrated by FIG. 30, the position indicator signal P, generated bythe position signal generator 420, may be processed in parallel with thefiltering 240, enveloping 250 and decimation 310 in a manner so as tosubstantially maintain an initial time relation between positive edgesof the position indicator signal P and corresponding vibration samplevalues Se(i) and S(j). This parallel processing of the positionindicator signal P originating from position signal generator 420 andthe vibration sample values originating from the vibration signal sensor10 advantageously ensures that any delay due to signal processing willaffect the position indicator signal values P(i) and the correspondingvibration sample values Se(i) in a substantially equal degree. Ineffect, the apparatus 14, 920 is adapted to process the positionindicator signal P so as to maintain an initial time relation betweenthe position indicator signal values P(i) and corresponding vibrationsample values Se(i) from the time of detection by the respective sensors420 and 10, respectively, up to the time of delivery of the timesequence of measurement sample values Se(i) of said digital measurementdata signal S_(RED1) (See FIG. 30 in conjunction with FIG. 19C).

Hence, the speed value generator 610 may be adapted to receive vibrationsample values Se(i) and corresponding position indicator signal valuesP(i) from the integer Decimator 310. As discussed in connection withFIGS. 19B and 19C, the speed value generator 601 is adapted to receive asequence of measurement values Se(i) and a sequence of positionalsignals P(i), together with temporal relations there-between, and thespeed value generator 601 is adapted to provide, on its output, asequence of pairs SP of measurement values S(j) associated withcorresponding speed values f_(ROT)(j).

These pairs SP of measurement values S(j) and corresponding speed valuesf_(ROT)(j) may be delivered to inputs of the fractional decimator 470,470B, 94 as illustrated in FIG. 30.

The output 312 of integer Decimator 310 may also be coupled to an inputof a selector 460. The selector enables a selection of the signal to beinput to the enhancer 320.

When condition monitoring is made on a rotating part having a constantspeed of rotation, the selector 460 may be set in the position todeliver the signal S_(RED) having sample frequency f_(SR1) to the input315 of enhancer 320, and fractional decimator 470 may be disabled. Whencondition monitoring is made on a rotating part having a variable speedof rotation, the fractional decimator 470 may be enabled and theselector 460 is set in the position to deliver the signal S_(RED2)having sample frequency f_(RED2) to the input 315 of enhancer 320.

The fractional decimator 470 may be embodied by fractional decimator470B, 94 including an adaptable FIR filter 608, as described inconnection with FIGS. 20, 21 and 22 and FIG. 4.

The fractional decimator 470 is coupled to deliver a decimated signalS_(RED2) having the lower sample rate f_(SR2) to the selector 460, sothat when the condition analyzer is set to monitor a machine withvariable speed of rotation, the output from fractional decimator 470B isdelivered to enhancer 320.

Enhancer 320, 94 may be embodied as described in connection with FIGS.10A, 10B, 11, 12 and 13 and FIG. 4. The measuring signal input to theenhancer 320 is the signal S_(RED) (See FIG. 30), which is alsoillustrated in FIG. 11 as having I_(LENGTH) sample values. The signalS_(RED) is also referred to as I and 2060 in the description of FIG. 11.The Enhancer signal processing involves discrete autocorrelation for thediscrete input signal S_(RED). According to an embodiment the enhanceroperates in the time domain so as to achieve discrete autocorrelationfor the discrete input signal S_(RED). Hence, according to thatembodiment, the enhancer signal processing does not include Fouriertransformation nor does it include any Fast Fourier Transform. Theoutput signal O, also referred to as S_(MDP), is illustrated in FIGS. 12and 13.

The measurement signal S_(RED), S_(RED1), to be input to the enhancer,may include at least one vibration signal component SD dependent on avibration movement of said rotationally movable part; wherein saidvibration signal component has a repetition frequency f_(D) whichdepends on the speed of rotation f_(ROT) of said first part. Therepetition frequency f_(D) of signal component SD may be proportional tothe speed of rotation f_(ROT) of the monitored rotating part.

Two different damage signatures SD1, SD2 may have different frequenciesfd1, fd2 and still be enhanced, i.e. SNR-improved, by the enhancer.Hence, the enhancer 320 is advantageously adapted to enhance differentsignatures S_(D1) and S_(D2) having mutually different repetitionfrequencies f_(D1) and f_(D2). Both of the repetition frequencies f_(D1)and f_(D2) are proportional to the speed of rotation f_(ROT) of themonitored rotating part, while f_(D1) is different from f_(D2) (f_(D1)<>f_(D1)). This may be expressed mathematically in the following manner:

fD1=k1*f _(ROT), and

fD2=k2*f _(ROT), wherein

-   -   k1 and k2 are positive real values, and    -   k1< >k2, and    -   k1 greater than or equal to one (1), and    -   k2 greater than or equal to one (1)

The enhancer delivers an output signal sequence to an input of timedomain analyzer 290T, so that when a user selects, via user interface102,104 to perform a time domain analysis, the time domain analyzer290T, 105 (FIG. 30 & FIG. 4) will execute the selected function 105 anddeliver relevant data to the display 106. An advantage with the enhancer320 is that it delivers the output signal in the time domain. Hence,condition monitoring functions 105, 290T requiring an input signal inthe time domain can be set to operate directly on the signal values ofthe signal output illustrated in FIGS. 12 and 13.

When a user selects, via user interface 102,104 to perform a frequencydomain analysis, the enhancer will deliver the output signal sequence toFast Fourier Transformer 294, and the FFTransformer will deliver theresulting frequency domain data to the frequency domain analyzer 290F,105 (FIG. 30 & FIG. 4). The frequency domain analyzer 290F, 105 willexecute the selected function 105 and deliver relevant data to thedisplay 106.

In the embodiment shown in FIGS. 29 and 30, it is advantageously easyfor a user to do perform an analysis employing the enhancer and thefractional decimator. As illustrated in FIG. 30, the user interface 102,104, 24B cooperates with a parameter controller 930 adapted to providesettings for the arrangement 920. FIG. 31 is a schematic illustration ofthe parameter controller 930.

The below is an example of parameter settings:

In order to perform an analysis in the frequency domain the user mayinput the following data via user interface 102,104 24B:

-   -   1) Information indicative of the highest repetition frequency        f_(D) of interest. The repetition frequency f_(D) is repetition        frequency a signature SD of interest. This information may be        input in the form of a frequency or in the form an order number        O_(VHigh) indicative of the highest repetition frequency of        damage signature SD of interest.    -   2) Information indicative of the desired improvement of the SNR        value for repetitive signal signature SD. This information may        be input in the form the SNR Improver value L. The SNR Improver        value L is also discussed below, and in connection with FIG. 10A        above.    -   3) Information indicative of the desired frequency resolution in        the FFT 294, when it is desired to perform an FFT of the signal        output from enhancer. This may be set as value Z frequency bins.        According to an embodiment of the invention, the frequency        resolution Z is settable by selecting one value Z from a group        of values. The group of selectable values for the frequency        resolution Z may include    -   Z=400    -   Z=800    -   Z=1600    -   Z=3200    -   Z=6400

Hence, although the signal processing is quite complex, the arrangement920 has been designed to provide an advantageously simple user interfacein terms of information required by the user. When the user inputs orselects values for the above three parameters, all the other values areautomatically set or preset in the arrangement 920.

The SNR Improver Value L

The signal to be input to the enhancer may include a vibration signalcomponent dependent on a vibration movement of the rotationally movablepart; wherein said vibration signal component has a repetition frequencyf_(D) which depends on the speed of rotation f_(ROT) of said first part;said measurement signal including noise as well as said vibration signalcomponent so that said measurement signal has a first signal-to-noiseratio in respect of said vibration signal component. The enhancerproduces an output signal sequence (O) having repetitive signalcomponents corresponding to said at least one vibration signal componentso that said output signal sequence (O) has a second signal-to-noiseratio value in respect of said vibration signal component. The inventorhas established by measurements that the second signal-to-noise ratiovalue is significantly higher than the first signal-to-noise ratio whenthe SNR Improver value L is set to value one (1).

Moreover, the inventor has established by measurements that when the SNRImprover value L is increased to L=4, then the resulting SNR value inrespect of said vibration signal component in the output signal isdoubled as compared to the SNR value associated with L=1. Increasing theSNR Improver value L to L=10 appears to render an improvement of theassociated SNR value by a factor 3 for the vibration signal component inthe output signal, as compared to the SNR value for same input signalwhen L=1. Hence, when increasing SNR Improver value L from L₁=1 to L₂the resulting SNR value may increase by the square root of L₂.

Additionally the user may input a setting to have the arrangement 920keep repeating the measurement. The user may set it to repeat themeasurement with a certain repetition period T_(PM), i.e. to alwaysstart a new measurement when the time T_(PM) has passed. T_(PM) may beset to be a one week, or one hour or ten minutes. The value to selectfor this repetition frequency depends on the relevant measuringconditions.

Since the enhancer method requires a lot of data input values, i.e. thenumber of input sample values may be high, and it is suited formeasuring on slowly rotating parts, the duration of the measurement willsometimes be quite long. Hence there is a risk that the user settingsfor the frequency of repetition of measurements is incompatible with theduration of measurements. Therefore, one of the steps performed by thearrangement 920, immediately after receiving the above user input, is tocalculate an estimate of the expected duration of measurements T_(M).

The duration T_(M) is:

T _(M) =I _(Length) /f _(SR2),

Wherein I_(Length) is the number of samples in the signal to be inputinto the enhancer in order to achieve measurements according to selecteduser settings as defined below, and f_(SR2) is as defined below.

The arrangement 920 is also adapted to compare the duration ofmeasurements T_(M) with the repetition period value T_(PM) as selectedby the user. If the repetition period value T_(PM) is shorter or aboutthe same as the expected duration of measurements T_(M), a parametercontroller 930 is adapted to provide a warning indication via the userinterface 102, 106 e.g. by a suitable text on the display. The warningmay also include a sound, or a blinking light.

According to an embodiment the arrangement 920 is adapted to calculate asuggested minimum value for the repetition period value T_(PM) isdependence on the calculated estimate of duration of measurements T_(M).

Based on the above user settings, the parameter controller 930 of signalprocessing arrangement 920 is capable of setting all the parameters forthe signal processing functions 94 (FIG. 4), i.e. integer decimatorsettings and enhancer settings.

Moreover the parameter controller 930 is capable of setting all theparameters for the fractional decimator when needed. The parametercontroller 930 is capable of setting the parameter for the FFT 294 whena frequency analysis is desired.

The following parameter may be preset in the arrangement 920 (FIG. 30):

Sample frequency f_(S) of A/D converter 40,44.

The following parameter may be measured: f_(ROT)

As mentioned above, the parameter value f_(ROT) may be measured andstored in association with the corresponding sample values of the signalS_(RED1) whose sample values are fed into the fractional decimator 470B.

The following parameters may be automatically set in the arrangement920:

Sample rate in the signal output from enhancer 320:

f _(SR2) =C*O _(V) *f _(ROT)

-   -   wherein    -   C is a constant of value higher than 2,0    -   O_(V) is the order number input by the user, or calculated in        response to a highest frequency value to be monitored as        selected by the user    -   f_(ROT) is the momentary measured rotational speed of the        rotating part during the actual condition monitoring;

M=The integer decimator value for use in decimator 310 is selected froma table including a set of predetermined values for the total integerdecimation. In order to select the most suitable value M, the parametercontroller 930 (FIG. 30) first calculates a fairly close value

M_calc=f _(S) /f _(SR2) *f _(ROTmin) /f _(ROTmax)

wherein

-   -   f_(S) & f_(SR2) are defined above, and    -   f_(ROTmin)/f_(ROTmax) is a value indicative of the relation        between lowest and highest speed of rotation to be allowed        during the measurement. Based on the value M_calc the selector        then choses a suitable value M from a list of preset values.        This may e.g be done by selecting the closest value M which is        lower than M_calc from the table mentioned above.    -   f_(SR1)=the sample rate to be delivered from the integer        decimator 310. f_(SR1) is set to

f _(SR1) =f _(S) /M

-   -   D is the fractional decimator value for fractional decimator. D        may be set to D=fsr1/fsr2, wherein fsr1 and fsr2 are as defined        above.

O _(LENGTH) =C*z

wherein

-   -   C is a constant of value higher than 2,0, such as e.g. 2,56 as        mentioned above    -   Z is the selected number of frequency bins, i.e. information        indicative of the desired frequency resolution in the FFT 294,        when it is desired to perform an FFT of the signal output from        enhancer.

S_(START)=O_(LENGTH) or a value higher than O_(LENGTH), whereinO_(LENGTH) is as defined immediately above.

I _(Length) =O _(LENGTH) *L+S _(START) +O _(LENGTH)

C _(Length) =I _(LENGTH) −S _(START) −O _(LENGTH)

S_(MDP)(t)=the values of the samples of the output signal, as defined inequation (5) (See FIG. 10A).

Hence, the parameter controller 930 is adapted to generate thecorresponding setting values as defined above, and to deliver them tothe relevant signal processing functions 94 (FIG. 30 & FIG. 4).

Once an output signal has been generated by enhancer 320, the conditionanalyser 290 can be controlled to perform a selected condition analysisfunction 105, 290, 290T, 290F by means of a selection signal deliveredon a control input 300 (FIG. 30). The selection signal delivered oncontrol input 300 may be generated by means of user interaction with theuser interface 102 (See FIGS. 2A & 30). When the selected analysisfunction includes Fast Fourier Transform, the analyzer 290F will be setby the selection signal 300 to operate on an input signal in thefrequency domain.

The FFTransformer 294 may be adapted to perform Fast Fourier Transformon a received input signal having a certain number of sample values. Itis advantageous when the certain number of sample values is set to aneven integer which may be divided by two (2) without rendering afractional number.

According to an advantageous embodiment of the invention, the number ofsamples O_(LENGTH) in the output signal from the enhancer is set independence on the frequency resolution Z. The relation between frequencyresolution Z and the number of samples O_(LENGTH) in the output signalfrom the enhancer is:

OLENGTH=k*z

Wherein

-   -   O_(LENGTH) is the samples number of sample values in the signal        delivered from the enhancer 320.    -   k is a factor having a value higher than 2,0

Preferably factor k may be selected to a value between 2,0 and 2,9 inorder to provide a good safety margin while avoiding to generateunnecessarily many sample values.

According to an embodiment the factor k is advantageously selected suchthat 100*k/2 renders an integer. This selection renders values forO_(LENGTH) that are adapted to be suitable as input into theFFTransformer 294. According to an embodiment the factor k may be set to2,56. Selecting k to 2,56 renders 100*k=256=2 raised to 8.

Table A indicates examples of user selectable Frequency resolutionvalues Z and corresponding values for O_(LENGTH).

TABLE A k Z O_(LENGTH) 2.56 400 1024 2.56 800 2048 2.56 1600 4096 2.563200 8192 2.56 6400 16384 2.56 12800 32768 2.56 25600 65536 2.56 51200131072

An embodiment of the invention relates to an apparatus for analysing thecondition of a machine having a first part which is rotationally movableat a speed of rotation in relation to a second machine part; saidapparatus including:

a sensor for monitoring said movable part so as to generate at least oneanalogue measurement signal including at least one vibration signalcomponent dependent on a vibration movement of said rotationally movablepart; wherein said vibration signal component has a repetition frequency(f_(D)) which depends on the speed of rotation (f_(ROT)) of said firstpart; said measurement signal including noise as well as said vibrationsignal component so that said measurement signal has a firstsignal-to-noise ratio value in respect of said vibration signalcomponent;

an A/D-converter (40,44) for generating a digital measurement datasequence (S_(MD)) in response to said measurement signal; said digitalmeasurement data sequence (S_(MD)) having a first sample rate (f_(S));

a first digital filter (240) for performing digital filtering of thedigital measurement data sequence (S_(MD)) so as to obtain a filteredmeasurement signal (S_(F));

an envelopper for generating a first digital signal (S_(ENV), S_(MDP))in response to the filtered measurement signal (S_(F));

a decimator for performing a decimation of the first digital signal(S_(ENV), S_(MDP)) so as to achieve a decimated digital signal (S_(RED))having a reduced sampling frequency (f_(SR1), f_(SR2));

said decimator (470, 470A, 470B) having

-   -   a first input for receiving said first digital signal (S_(ENV),        S_(MDP)); and    -   a second input for receiving a signal indicative of said        variable speed of rotation (f_(ROT));    -   a third input for receiving a signal indicative of an output        sample rate setting signal;    -   said decimator (470, 470A, 470B) being adapted to generate said        decimated digital signal (S_(RED)) in dependence on    -   said first digital signal (S_(MD), S_(ENV)),    -   said signal indicative of said speed of rotation (f_(ROT)), and    -   said signal indicative of an output sample rate setting signal;        wherein said decimator (470, 470A, 470B) is adapted to generate        said decimated digital signal (S_(RED)) such that the number of        sample values per revolution of said rotating part is kept at a        substantially constant value when said speed of rotation varies;        and

an enhancer (320) having an input for receiving said decimated digitalsignal (S_(RED)); said enhancer being adapted to produce an outputsignal sequence (O) having repetitive signal components corresponding tosaid at least one vibration signal component so that said output signalsequence (O) has a second signal-to-noise ratio value in respect of saidvibration signal component; said second signal-to-noise ratio valuebeing higher than said first signal-to-noise ratio value; and ananalyzer (105; 290; 290T; 294, 290F) for indicating a machine conditiondependent on said vibration movement of said rotationally movable partin response to said output signal sequence (O). This solutionadvantageously provides a very lean solution by minimizing thecomplexity of filters while achieving significant performanceimprovement.

Various embodiments are disclosed below.

An embodiment E1 comprises: A method for analysing the condition of amachine having a rotating part, comprising:

generating a position signal (P, P_((i)); P₍₁₎, P₍₂₎, P₍₃₎, Ep)indicative of a rotational position of said rotating part;

generating an analogue measurement signal (S_(EA)) dependent onmechanical vibrations emanating from rotation of said part;

sampling said analogue measurement signal (S_(EA)) so as to generate adigital measurement data signal (S_(MD)), having a sampling frequency(f_(S), f_(SR1)), in response to said analogue measurement signal(S_(EA));

performing a decimation of the digital measurement data signal (S_(MD))so as to achieve a digital signal (S_(RED1), S_(RED2)) having a reducedsampling frequency (f_(SR2));

performing a condition analysis function (F1, F2, Fn) for analysing thecondition of the machine dependent on said digital signal (S_(RED1),S_(RED2), O) having a reduced sampling frequency (f_(SR1), f_(SR2));wherein

said decimation includes

-   -   recording a time sequence of measurement sample values (Se(i),        S_((j))) of said digital measurement data signal (S_(RED1),        S_(MD)) and    -   recording a time sequence of position signal values (P_((i))) of        said position signal (Ep) such that there is    -   a first temporal relation (n_(diff), n_(diff1), n_(diff2))        between at least some of the recorded position signal values        (P_((i))), and such that there is    -   a second temporal relation between at least one of the recorded        position signal values (P_((i))) and at least one of the        recorded measurement sample values (Se(i), S_((j));

generating a value indicative of an acceleration (a, a₁₋₂, a₂₋₃) of saidrotational part (8) in dependence of said first temporal relation(n_(diff), n_(diff1), n_(diff2));

generating a speed value (VT1, VT2, f_(ROT)) indicative of a momentalyspeed of rotation of said of said rotational part (8) in dependence of

-   -   said value indicative of an acceleration (a, a₁₋₂, a₂₋₃) and    -   a certain time value

such that the speed value (VT 1, VT2, f_(ROT)) is indicative of therotational speed at the moment of detection of at least one of saidrecorded measurement sample values (Se(i), S_((j)); and wherein

said decimation is performed dependent on said speed value (VT1, VT2,f_(ROT))

Embodiment E2

The method according to embodiment E1, wherein Said certain time valuedepends on said second temporal relation.

Embodiment E3

The method according to embodiment E1, wherein Said certain time valueis said second temporal relation.

Embodiment E4

A method for analysing the condition of a machine having a rotatingpart, comprising:

generating a position signal (Ep) indicative of a rotational position ofsaid rotating part;

generating an analogue measurement signal (S_(EA)) dependent onmechanical vibrations emanating from rotation of said part;

sampling said analogue measurement signal (S_(EA)) so as to generate adigital measurement data signal (S_(MD)), having a sampling frequency(f_(S), f_(SR1)), in response to said analogue measurement signal(S_(EA));

performing a decimation of the digital measurement data signal (S_(MD))so as to achieve a digital signal (S_(RED2)) having a reduced samplingfrequency (f_(SR2));

performing a condition analysis function (F1, F2, Fn) for analysing thecondition of the machine dependent on said digital signal (S_(RED),S_(RED2), O) having a reduced sampling frequency (f_(SR1), f_(SR2));wherein

wherein said decimation includes

-   -   recording a time sequence of measurement sample values (Se(i),        S_((j))) of said digital measurement data signal (S_(MD)) and    -   recording a time sequence of position signal values (P_((i))) of        said position signal (Ep) such that there is        -   a first temporal relation (n_(diff), n_(diff1), n_(diff2))            between at least some of the recorded position signal values            (P_((i))), and such that there is        -   a second temporal relation between at least one of the            recorded position signal values (P_((i))) and at least one            of the recorded measurement sample values (Se(i), S_((j)));

generating a value indicative of a speed change (df_(ROT), a, a₁₋₂,a₂₋₃) of said rotational part (8) in dependence of said first temporalrelation (n_(diff), n_(diff1), n_(diff2));

generating a speed value indicative of a momentary speed of rotation ofsaid of said rotational part (8) in dependence of

-   -   said value indicative of a speed change (df_(ROT), a, a₁₋₂,        a₂₋₃) and    -   a certain time value

such that the speed value is indicative of the rotational speed at themoment of detection of at least one of said recorded measurement samplevalues (Se(i), S_((j))); and wherein

said decimation is performed dependent on said speed value (VT1, VT2,

Embodiment E5

The method according to embodiment E4, wherein

Said certain time value depends on said second temporal relation.

Embodiment E6

The method according to embodiment E4, wherein Said certain time valueis said second temporal relation.

Embodiment E7

The method according to any preceding embodiment E1 to E6, wherein thestep of

recording a time sequence of position signal values (P_((i))) of saidposition signal (Ep) comprises the steps of:

-   -   recording a first position signal value (P1 _((i))) of said        position signal (Ep) and information indicative of the time of        occurrence of said first position signal value (P1 _((i)));    -   recording a second position signal value (P2 _((i))) of said        position signal (Ep) and information indicative of the time of        occurrence of said second position signal value (P2 _((i)));

the method further including the step of:

establishing a first speed value (VT1) indicative of a momentary speedof rotation of said of said rotational part (8) at a first moment intime between the occurrence of said first position signal value (P1_((i))) and the occurrence of said second position signal value (P2_((i))).

Embodiment E8

The method according to embodiment E7,

identifying a selected recorded measurement data value (S(j)), and

identifying the moment of detection (i, j) of said selected recordedmeasurement data value (Se(i), S(j));

establishing a value (delta-t) indicative of a first duration of timefrom said first moment to said moment of detection (i, j) of saidselected recorded measurement data value (Se(i), S(j));

Establishing a second speed value (Vp30, Vp40, Vp50, Vp60, f_(ROT))indicative of a momentary speed of rotation of said rotational part atsaid moment of detection (i, j) in dependence on

-   -   said first speed value (VT1), said first duration and    -   information indicative of a speed change during said first        duration.

Embodiment E9

The method according to embodiment E8, wherein

Said information indicative of a speed change during said first durationis said value indicative of an acceleration (a, a₁₋₂, a₂₋₃).

Embodiment E10

The method according to embodiment E8, wherein

Said information indicative of a speed change during said first durationis said value indicative of a speed change (df_(ROT), a, a₁₋₂, a₂₋₃).

Embodiment E11

The method according to any preceding embodiment E1 to E10, wherein thestep of performing a condition analysis function (F1, F2, Fn) includes

performing an autocorrelation of said digital signal (S_(RED), S_(RED2))having a reduced sampling frequency (f_(SR1), f_(SR2)) so as to obtainan autocorrelated digital signal (0) having a reduced sampling frequency(f_(SR2)); and

performing analysis function (F1, F2, Fn, 290T) using the autocorrelateddigital signal (0) as input to the condition analyser (290T).

Embodiment E12

The method according to any preceding embodiment E1 to E11, wherein thestep of performing a condition analysis function (F1, F2, Fn) includes

performing an autocorrelation of said digital signal (S_(RED), S_(RED2))having a reduced sampling frequency (f_(SR1), f_(SR2)) so as to obtainan autocorrelated digital signal (0) having a reduced sampling frequency(f_(SR2)); and

performing a fast fourier transform (294, 94), using the autocorrelateddigital signal (0) as input to the fast fourier transformer (294, 94),so as to obtain an autocorrelated digital signal in the frequencydomain; and

performing analysis function (F1, F2, Fn, 290F) using the autocorrelateddigital signal in the frequency domain as input to the conditionanalyser (290F).

Embodiment E13

An apparatus for analysing the condition of a machine having a partrotating with a speed of rotation (f_(ROT)), comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(S)) so as to generate a digital measurement data signal(S_(MD), S_(ENV)) in response to said received analogue electricmeasurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part;

a first decimator (310) for performing a decimation of the digitalmeasurement data signal (S_(MD), S_(ENV)) so as to achieve a firstdigital signal (S_(RED1)) having a first reduced sampling frequency(f_(SR1)) such that the first reduced sampling frequency (f_(SR1)) isreduced by an integer factor (M) as compared to the initial samplingfrequency (f_(S));

a second decimator (470, 470B) for generating a second digital signal(S_(RED2), R), having a second reduced sampling frequency (f_(SR2)), inresponse to said first digital signal (S_(RED1)), and

an evaluator (230; 290, 290T; 294, 290, 290F) for performing a conditionanalysis function (F1, F2, Fn) for analysing the condition of themachine dependent on said second digital signal (SRE₀₂) having a reducedsampling frequency (f_(SR1), f_(SR2)); wherein

a speed value generator is adapted for recording a time sequence ofmeasurement sample values (Se(i), S_((j))) of said digital measurementdata signal (S_(MD)) and

-   -   said speed value generator being adapted for recording a time        sequence of said position signal values (P_((i))) of said        position signal (Ep) such that there is        -   a first temporal relation (n_(diff), n_(diff1), n_(diff2))            between at least some of the recorded position signal values            (P_((i))), and such that there is        -   a second temporal relation between at least one of the            recorded position signal values (P_((i))) and at least one            of the recorded measurement sample values (Se(i), S_((j)));

said speed value generator being adapted for generating a valueindicative of an acceleration (a, a₁₋₂, a₂₋₃) of said rotational part(8) in dependence of said first temporal relation (n_(diff), n_(diff1),n_(diff2));

said speed value generator being adapted for generating a speed value(VT1, VT2, f_(ROT)) indicative of a momentary speed of rotation of saidof said rotational part (8) in dependence of

-   -   said value indicative of an acceleration (a, a₁₋₂, a₂₋₃) and    -   a certain time value

such that the speed value (VT1, VT2, f_(ROT)) is indicative of therotational speed at the moment of detection of at least one of saidrecorded measurement sample values (Se(i), S_((j))); and wherein

said second decimator (470, 470B) is adapted to perform said decimationdependent on said speed value (VT1, VT2, f_(ROT)).

Embodiment E14

An apparatus for analysing the condition of a machine having a partrotating with a speed of rotation (f_(ROT)), comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(S)) so as to generate a digital measurement data signal(S_(MD), S_(ENV)) in response to said received analogue electricmeasurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part;

a first decimator (310) for performing a decimation of the digitalmeasurement data signal (S_(MD), SENO so as to achieve a first digitalsignal (S_(RED1)) having a first reduced sampling frequency (f_(SR1))such that the first reduced sampling frequency (f_(SR1)) is reduced byan integer factor (M) as compared to the initial sampling frequency(f_(S));

a second decimator (470, 470B) for generating a second digital signal(S_(RED2), R), having a second reduced sampling frequency (f_(SR2)), inresponse to said first digital signal (S_(RED1)), and

an evaluator (230; 290, 290T; 294, 290, 290F) for performing a conditionanalysis function (F1, F2, Fn) for analysing the condition of themachine dependent on said second digital signal (S_(RED2)) having areduced sampling frequency (f_(SR1), f_(SR2)); wherein

-   -   a speed value generator is adapted for recording a time sequence        of measurement sample values (Se(i), S_((j))) of said digital        measurement data signal (S_(MD)); wherein    -   said speed value generator is adapted for recording a time        sequence of position signal values (P_((i))) of said position        signal (Ep) such that there is    -   a first temporal relation (n_(diff), n_(diff1), n_(diff2))        between at least some of the recorded position signal values        (P_((i))), and such that there is    -   a second temporal relation between at least one of the recorded        position signal values (P_((i))) and at least one of the        recorded measurement sample values (Se(i), S_((j)));

wherein

said speed value generator is adapted for generating a value indicativeof a speed change (df_(ROT), a, a₁₋₂, a₂₋₃) of said rotational part (8)in dependence of said first temporal relation (n_(diff), n_(diff1),n_(diff2)); and

said speed value generator is adapted for generating a speed valueindicative of a momentary speed of rotation of said of said rotationalpart (8) in dependence of

said value indicative of a speed change (dfROT, a, a₁₋₂, a₂₋₃) and

a certain time value

such that the speed value is indicative of the rotational speed at themoment of detection of at least one of said recorded measurement samplevalues (Se(i), _((j))); and wherein

said second decimator (470, 470B) is adapted to perform said decimationdependent on said speed value (VT1, VT2, f_(ROT)).

Embodiment E15

An apparatus for analysing the condition of a machine having a partrotating with a speed of rotation (f_(ROT)), comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(S)) so as to generate a digital measurement data signal(S_(MD), S_(ENV)) in response to said received analogue electricmeasurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part;

-   -   a speed value generator (601) being adapted for recording a time        sequence of measurement sample values (Se(i), S_((j))) of said        digital measurement data signal (S_(MD));

wherein

-   -   said speed value generator is adapted for recording a time        sequence of position signal values (P_((i))) of said position        signal (Ep) such that there is        -   a first temporal relation (n_(diff), n_(diff1), n_(diff2))            between at least some of the recorded position signal values            (P_((i))), and such that there is        -   a second temporal relation between at least one of the            recorded position signal values (P_((i))) and at least one            of the recorded measurement sample values (Se(i), S_((j)));            wherein

said speed value generator is adapted for generating a value indicativeof a speed change (df_(ROT), a, a₁₋₂, a₂₋₃) of said rotational part (8)in dependence of said first temporal relation (n_(diff), n_(diff1),n_(diff2)); and

said speed value generator is adapted for generating a speed valueindicative of a momentary speed of rotation of said of said rotationalpart (8) in dependence of

-   -   said value indicative of a speed change (df_(ROT), a, a₁₋₂,        a₂₋₃) and    -   a certain time value

such that the speed value is indicative of the rotational speed at themoment of detection of at least one of said recorded measurement samplevalues (Se(i), S_((j))).

Embodiment E16

An apparatus for analysing the condition of a machine having a partrotating with a speed of rotation (f_(ROT)), comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(S)) so as to generate a digital measurement data signal(S_(MD), S_(ENV)) in response to said received analogue electricmeasurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part; and

a speed value generator (601) being adapted for recording a timesequence of said position signal values (P_((i))) such that there is afirst temporal relation (n_(diff), n_(diff1), n_(diff2)) between atleast some of the recorded position signal values (P_((i))); wherein

-   -   said speed value generator comprises functionality adapted to        distinguish between a constant speed phase (S#30) and an        acceleration phase (S#40) in response to said a first temporal        relation (n_(diff), n_(diff1), n_(diff2)) between at least some        of the recorded position signal values (P_((i))).

Embodiment E17

An apparatus for analysing the condition of a machine having a partrotating with a speed of rotation (f_(ROT)), comprising:

a first sensor (10) adapted to generate an analogue electric measurementsignal (S_(EA)) dependent on mechanical vibrations (V_(MD)) emanatingfrom rotation of said part;

an analogue-to-digital converter (40, 44) adapted to sample saidanalogue electric measurement signal (S_(EA)) at an initial samplingfrequency (f_(S)) so as to generate a digital measurement data signal(S_(MD), S_(ENV)) in response to said received analogue electricmeasurement signal (S_(EA));

a device (420) for generating a position signal (Ep) having a sequenceof position signal values (P_((i))) for indicating momentary rotationalpositions of said rotating part; and

a speed value generator (601) being adapted for recording a timesequence of said position signal values (P_((i))) such that there areangular distances (delta-FI_(p1-p2), delta-FI_(p2-p3)) and correspondingdurations (delta-T_(p1-p2); delta-T_(p2-p3)) between at least threeconsecutive position signals (P1, P2, P3) wherein

-   -   the speed value generator (601) operates to establish at least        two momentary speed values (VT1; VT2) based on said angular        distances (delta-FI_(p1-p2), delta-FI_(p2-p3)) and said        corresponding durations (delta-T_(p1-p2); delta-T_(p2-p3)).

Embodiment E18

The apparatus according to embodiment E17, wherein

further momentary speed values for the rotational part (8) areestablished by interpolation between the at least two momentary speedvalues (VT1, VT2).

Embodiment E19

The apparatus according to embodiment E17, wherein

a speed difference (V_(Delta)) is generated in dependence on said atleast two momentary speed values (VT1; VT2), such as e.g. by calculationas

V _(Delta) =VT2−VT1

Embodiment E20

The apparatus according to embodiment E17, E18 or E19, wherein

-   -   the speed value generator (601) operates to establish (S#70) a        first speed of revolution value (VT1) in dependence of        -   the angular distance (delta-FI_(p1-p2)) between a first            positional signal (P1) and a second positional signal (P2),            and in dependence of        -   a corresponding first duration (delta-T_(p1-p2)); and            wherein the speed value generator (601) operates to            establish (S#100) a second momentary speed value (VT2) in            dependence of        -   the angular distance (delta-FI_(p2-p3)) between the second            positional signal (P2) and a third positional signal (P3),            and in dependence of

a corresponding second duration (delta-T_(p2-p3)).

Embodiment E21

The apparatus (14, 920) according to embodiment E20, wherein

-   -   the speed value generator (601) operates to assign (S#80) the        calculated first speed value (VT1, V_((t1))) to a first time        slot (t1) in the middle between the first positional signal (P1)        and the second positional signal (P2); and    -   wherein    -   the speed value generator (601) operates to assign (S#110) the        calculated second speed value (VT2, V_((t2))) to a second mid        time slot (t2) in the middle between the second positional        signal (P2) and the third positional signal (P3).

Embodiment E22

The apparatus (14, 920) according to embodiment E21 when includingembodiment E19, wherein

-   -   the speed difference (V_(Delta)) is divided by the number of        time slots between the second mid time slot and the first mid        time slot so as to generate a speed difference value dV        indicative of a speed difference between adjacent slots.

1. (canceled)
 2. A system for detecting an operating condition of amachine including a bearing associated with a shaft that rotates at avariable speed, the system comprising: a position sensor configured todetect a plurality of position values of the shaft; a vibration sensorconfigured to detect mechanical vibrations responsive to the rotation ofthe shaft with respect to the bearing; an analog to digital converterconfigured to generate a digital measurement data signal responsive tothe detected mechanical vibrations; and one or more hardware processorsconfigured to: detect at least two momentary speed values of the shaftbased on the detected plurality of position values of the shaft;generate an interpolated momentary speed value of the shaft based on aninterpolation between the at least two momentary speed values; decimate,after the interpolation and the generation of the interpolated momentaryspeed value, the digital measurement data signal based on the generatedinterpolated momentary speed value; and detect an operating condition ofthe machine based on the decimated digital measurement signal.
 3. Thesystem according to claim 2, wherein the interpolation comprises alinear interpolation.
 4. The system according to claim 2, wherein theinterpolation comprises a non-linear interpolation.
 5. The systemaccording to claim 2, wherein the operating condition is detected basedon an autocorrelation of the decimated digital measurement data signal.6. A method of detecting an operating condition of a machine including abearing associated with a shaft that rotates at a variable speed, themethod comprising: detecting a plurality of position values of theshaft; detecting mechanical vibrations responsive to the rotation of theshaft with respect to the bearing; generating a digital measurement datasignal responsive to the detected mechanical vibrations; detecting atleast two momentary speed values of the shaft based on the detectedplurality of position values of the shaft; generating an interpolatedmomentary speed value of the shaft based on an interpolation between theat least two momentary speed values; decimating, after the interpolationand the generation of the interpolated momentary speed value, thedigital measurement data signal based on the generated interpolatedmomentary speed value; and detecting an operating condition of themachine based on the decimated digital measurement signal.
 7. A systemfor detecting an operating condition of a machine including a bearingassociated with a shaft that rotates at a variable speed, the systemcomprising one or more hardware processors configured to: detect atleast two momentary speed values of the shaft based on a plurality ofposition values of the shaft; generate an interpolated momentary speedvalue of the shaft based on an interpolation between the at least twomomentary speed values; decimate, after the interpolation and thegeneration of the interpolated momentary speed value, a digitalmeasurement data signal based on the generated interpolated momentaryspeed value, said mechanical signal responsive to detected vibrationsfrom a vibration sensor; and detect an operating condition of themachine based on the decimated digital measurement signal.